Income Taxes - Tax Carryforwards and Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Operating Loss and Tax Credit Carryforwards [Line Items]
Net operating loss carryforwards	$ 380	$ 350
Tax credit carryforwards	3,406	$ 3,259
Federal [Member]
Operating Loss and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	3,060
State [Member]
Operating Loss and Tax Credit Carryforwards [Line Items]
Net operating loss carryforwards	304
Tax credit carryforwards	344
Tax credit carryforward with indefinite expiration period	188
Foreign [Member]
Operating Loss and Tax Credit Carryforwards [Line Items]
Net operating loss carryforwards	76
Tax credit carryforwards	2
Operating loss carryforwards with indefinite expiration period	$ 58