Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Difference between income taxes computed at the U.S. federal statutory income tax rate and the income tax expense (benefit)
Federal income tax provision at statutory rate	$ 394	$ 403	$ 387
Federal income tax provision at statutory rate	21.00%	35.00%	35.00%
State taxes, net of federal benefit	$ 36	$ 4	$ 9
State taxes, net of federal benefit	2.00%	0.00%	1.00%
Research and development credits	$ (46)	$ (26)	$ (36)
Research and development credits	(2.00%)	(2.00%)	(3.00%)
Foreign rate differential	$ (198)	$ (271)	$ (239)
Foreign rate differential	(11.00%)	(24.00%)	(22.00%)
Change in tax reserves	$ 265	$ 291	$ 210
Change in tax reserves	14.00%	25.00%	19.00%
Audit settlements	$ (115)	$ 0	$ 0
Audit settlements	(6.00%)	0.00%	0.00%
Net operating loss tax attribute assumed from the Purchase Transaction	$ 0	$ (36)	$ (114)
Net operating loss tax attribute assumed from the Purchase Transaction	(0.00%)	(3.00%)	(10.00%)
Excess tax benefits related to share-based payments	$ (58)	$ (113)	$ (81)
Excess tax benefits related to share-based payments	(3.00%)	(10.00%)	(7.00%)
U.S. Tax Reform Act	$ (285)	$ 636	$ 0
U.S. Tax Reform Act	(15.00%)	55.00%	0.00%
Change in valuation allowance	$ 61	$ 0	$ 0
Change in valuation allowance	3.00%	0.00%	0.00%
Other	$ 10	$ (10)	$ 4
Other	0.00%	0.00%	0.00%
Income tax expense	$ 64	$ 878	$ 140
Income tax expense	3.00%	76.00%	13.00%