Income per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Income from continuing operations	$ 969	$ 931	$ 856
Discontinued operations	2,077	822	726
Net income	$ 3,046	$ 1,753	$ 1,582
Weighted average common shares outstanding, basic	680	705	706
Effect of dilutive securities	3	4	4
Weighted average common shares outstanding, diluted	683	709	710
Basic:
Income from continuing operations (in dollars per basic share)	$ 1.42	$ 1.32	$ 1.21
Discontinued operations (in dollars per basic share)	$ 3.06	$ 1.17	$ 1.03
Net income (in dollars per basic share)	$ 4.48	$ 2.49	$ 2.24
Diluted:
Income from continuing operations (in dollars per diluted share)	$ 1.42	$ 1.31	$ 1.21
Discontinued operations (in dollars per diluted share)	$ 3.04	$ 1.16	$ 1.02
Net income (in dollars per diluted share)	$ 4.46	$ 2.47	$ 2.23
Antidilutive securities excluded from computation of earnings per share	4	5	10