Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Participating Securities, Distributed and Undistributed Earnings		$ 6	$ 4	$ 18	$ 13
Antidilutive securities excluded from computation of earnings per share		3.5	4.1	2.4	2.8
Numerator for earnings per share calculations:
Income from continuing operations attributable to common stockholders	[1]	$ 1,230	$ 944	$ 3,711	$ 3,310
Denominators for earnings per share calculations:
Weighted averages shares outstanding, basic (in shares)		1,114.0	1,157.0	1,122.0	1,167.0
Effect of dilutive securities
Stock options (in shares)		7.0	7.0	8.0	8.0
Weighted averages shares outstanding, diluted (in shares)		1,121.0	1,164.0	1,130.0	1,175.0
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share		$ 1.10	$ 0.82	$ 3.31	$ 2.84
Diluted earnings per share:
Income (Loss) from Continuing Operations, Per Diluted Share		$ 1.10	$ 0.81	$ 3.28	$ 2.82

[1] Comprised of income from continuing operations less net income attributable to noncontrolling interest and amounts allocable to participating securities of $6 million and $4 million for the three months ended September 30, 2015 and 2014, respectively, and $18 million and $13 million for the nine months ended September 30, 2015 and 2014, respectively.