Earnings per Common Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income (Numerator):
Net income	$ 192	$ 203
Earnings applicable to non-vested restricted stock	0	0
Net income applicable to common stock for computing basic earnings per common share	192	203
Net income as adjusted for purposes of computing diluted earnings per common share	$ 192	$ 203
Weighted average number of shares:
Outstanding during period (in shares)	566,687,000	578,197,000
Non-vested restricted stock (in shares)	(4,718,000)	(3,662,000)
Weighted average shares outstanding for computing basic earnings per common share (in shares)	561,969,000	574,535,000
Incremental common shares attributable to dilutive securities:
Shares issuable under convertible securities (in shares)	10,000	10,000
Shares issuable under incentive compensation plans (in shares)	1,526,000	911,000
Number of shares as adjusted for purposes of computing diluted earnings per common share (in shares)	563,505,000	575,456,000
Basic earnings per common share:
Basic earnings per common share (in dollars per share)	$ 0.34	$ 0.35
Diluted earnings per common share:
Diluted earnings per common share (in dollars per share)	$ 0.34	$ 0.35
Stock option awards
Diluted earnings per common share:
Number of shares of common stock excluded from the computation of diluted earnings per share (in shares)	2,200,000	3,100,000