Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income [Abstract]
Basic EPS									$ 2,024	$ 2,441	$ 1,384
Diluted EPS									$ 2,024	$ 2,441	$ 1,384
Shares [Abstract]
Basic EPS (in shares)									881,800,000	891,800,000	902,200,000
Stock options and restricted stock units (in shares)									6,000,000	6,600,000	7,500,000
Diluted EPS (in shares)									887,800,000	898,400,000	909,700,000
Earnings Per Share, Basic [Abstract]
Basic EPS (in dollars per share)	$ 0.37	$ 0.69	$ 0.59	$ 0.64	$ 0.68	$ 0.79	$ 0.67	$ 0.60	$ 2.30	$ 2.74	$ 1.53
Earnings Per Share, Diluted [Abstract]
Diluted EPS (in dollars per share)	$ 0.37	$ 0.68	$ 0.59	$ 0.64	$ 0.68	$ 0.78	$ 0.67	$ 0.59	$ 2.28	$ 2.72	$ 1.52
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									11,056,725	3,187,485	3,228,359
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									91	2,693	120