Income Taxes - Tax Carryforwards and Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Operating Loss and Tax Credit Carryforwards [Line Items]
Net operating loss carryforwards	$ 427	$ 604
Tax credit carryforwards	3,059	$ 2,916
Federal [Member]
Operating Loss and Tax Credit Carryforwards [Line Items]
Net operating loss carryforwards	165
Tax credit carryforwards	2,697
State [Member]
Operating Loss and Tax Credit Carryforwards [Line Items]
Net operating loss carryforwards	174
Tax credit carryforwards	362
Tax credit carryforward with indefinite expiration period	188
Foreign [Member]
Operating Loss and Tax Credit Carryforwards [Line Items]
Net operating loss carryforwards	88
Operating loss carryforwards with indefinite expiration period	$ 60