Summary of Significant Accounting Policies - Earnings Per Common Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Net income for common stock	$ 1,062	$ 1,138	$ 1,051
Weighted average common shares outstanding - Basic	292.9	292.9	292.6
Add: Incremental shares attributable to effect of potentially dilutive securities	1.5	1.6	1.8
Adjusted weighted average common shares outstanding - Diluted	294.4	294.5	294.4
Net income for common stock per common share - basic	$ 3.62	$ 3.88	$ 3.59
Net income for common stock per common share - diluted	$ 3.61	$ 3.86	$ 3.57