Common Stock (Details) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended
	May 31, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock			$ 400,000,000	$ 180,000,000
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)			10.0	5.4
Share repurchases program, authorized amount	1,000,000,000
Stock repurchase program, remaining authorized repurchase amount		$ 712,000,000