Common Stock (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	May. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 200,000,000	$ 300,000,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	3,500,000.0	5,300,000
Share repurchases program, authorized amount (up to)			$ 2,000,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 960,000,000