Common Stock (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 300,000,000	$ 100,000,000
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	5.3	2.0
Share repurchases program, authorized amount	2,000,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 1,000,000,000