The biggest U.S. advertiser has a new media chief as Procter & Gamble Co. has named Kristine Decker to oversee its estimated $3 billion-plus U.S. media outlay.

Ms. Decker, brand director-North America Brand Operations, had previously been brand director-North America Pet Care. P&G divested that business to Mars in August. She's been transitioning into the media role under Jodi Allen, former VP-North America Brand Operations. Ms. Allen has been overseeing North American media directly following departure of P&G's former top media executive Julie Eddleman to Google last year.

Ms. Allen became VP-North American Hair Care late last year and was handling both jobs for a time. That transition is now complete, a P&G spokeswoman said. Staffing and duties of the North American Brand Operations group have been reduced considerably following a reorganization last year that shifted much of the group's duties to the brand groups in P&G's global business units.

Post-reorganization, media buying and planning are the key marketing function that remains in North American Selling and Market Operations, which succeeded the old Market Development Organization.

Ms. Decker hadn't been a media specialist prior to her current role, but had a noteworthy media effort to her credit. She was the marketing executive on P&G's Walmart team who oversaw the company's "Family Movie Night" collaboration, in which P&G and the retailer jointly fronted production and created commercials for the TV movies that ran on NBC. That effort won a Bronze Effie in 2012. Previously, Ms. Decker had also been a brand manager on Swiffer.

P&G long has ranked as the biggest U.S. advertising spender, with nearly $5 billion in overall spending in 2013, according to the Ad Age Datacenter. P&G had $2 billion in measured media spending through the first nine months of 2014, down 16% from the same period a year ago, according to Kantar Media.

While P&G has acknowledged cutting media spending some last year, much of that decline likely owes to a shift into harder-to-measure digital media. Overall, P&G's global reported ad spending declined 4% to $9.2 billion for the fiscal year ended June 30.

Publicis Groupe's Starcom Mediavest Group handles media-buying duties for P&G in the U.S. and communications planning for most brands in North America. Carat, a unit of Dentsu Aegis Network, handles media buying in Canada and communications planning for some brands in North America.

Melanie Healey, once a CEO contender who had led P&G's North America operations overall, announced her retirement late last year. She's been succeeded by Carolyn Tastad, a longtime sales executive and the company's former global customer development officer, as group-president North America Selling and Market Operations. Ms. Decker will report directly to her.