Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
NUMERATOR:
Net income	$ 1,888	[1]	$ 503	$ 746	$ 351	$ 522	$ 388	$ 820	$ 513	$ 3,488	$ 2,244	$ 2,181
Incremental income effect of interest on 5.25% convertible notes										0	2	4
Net income after assumed conversion										$ 3,488	$ 2,246	$ 2,185
DENOMINATOR:
Weighted-average shares outstanding, basic										601	627	661
Dilutive effect of Employee stock options and restricted stock units										2	1	2
Dilutive effect of 5.25% convertible notes										0	5	6
Adjusted weighted-average shares outstanding, diluted										603	633	669
NET INCOME PER SHARE:
Basic (in dollars per share)	$ 3.19	[1]	$ 0.84	$ 1.24	$ 0.57	$ 0.85	$ 0.63	$ 1.30	$ 0.80	$ 5.80	$ 3.58	$ 3.30
Diluted (in dollars per share)	$ 3.18	[1]	$ 0.84	$ 1.23	$ 0.57	$ 0.84	$ 0.62	$ 1.28	$ 0.79	$ 5.79	$ 3.55	$ 3.27
Convertible Debt | 5.25% Convertible Senior Notes due 2016
Potentially dilutive amounts excluded from calculations:
Debt Instrument, Interest Rate, Stated Percentage	5.25%					5.25%				5.25%	5.25%	5.25%

[1] Includes a $1.4 billion reduction in Provision for income taxes related to the Tax Cuts and Jobs Act legislation enacted in December 2017, which resulted in a re-measurement of the Company's deferred tax assets and liabilities at the new federal corporate tax rate of 21 percent. See Note 14 to the Consolidated Financial Statements for further information.