Earnings Per Share - Reconciliation of Basic and Diluted Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share Reconciliation [Abstract]
Net income available to common shareholders	$ 491	$ 460	$ 457
Weighted average shares
Basic shares	120,000,000	121,000,000	121,000,000
Effect of dilutive securities—options outstanding	1,000,000	1,000,000	2,000,000
Diluted shares	121,000,000	122,000,000	123,000,000
Net income per share - Basic (in dollars per share)	$ 4.09	$ 3.80	$ 3.78
Net income per share - Diluted (in dollars per share)	$ 4.06	$ 3.77	$ 3.72
Antidilutive Shares Excluded From Earnings Per Share Calculation [Abstract]
Number of potential common shares excluded from the calculation of weighted average shares - considered to be antidilutive	1,000,000	1,000,000	0