Common Stock (Details) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended	3 Months Ended
	May 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock		$ 100,000,000	$ 100,000,000
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)		2.0	2.7
Share repurchases program, authorized amount	1,000,000,000
Stock repurchase program, remaining authorized repurchase amount		$ 463,000,000