Common Stock (Details) - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	May 31, 2015
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 410,000,000	$ 775,000,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	7,000,000.0	13,500,000
Payments for repurchase of common stock	$ 425,000,000
Common stock repurchased, incurred but not yet paid (in shares)	200,000
Payments for repurchase of common stock incurred but not yet paid	$ 15,000,000
Share repurchases program, authorized amount (up to)			$ 2,000,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 730,000,000