Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018
Income taxes
Income tax (benefit) expense	$ (84)	$ 60
Net discrete tax benefit	$ (98)	$ (8)
Estimated annual effective tax rate excluding impact of discrete items	20.90%	28.60%
Tax Cuts and Jobs Act (Tax Act)
Income taxes
Income tax (benefit) expense			$ 192
Tax Cuts and Jobs Act (Tax Act) | Taxation of Unremitted Foreign Earnings
Income taxes
Income tax (benefit) expense			$ 198
Period of tax payments on unremitted foreign earnings (in years)			8 years
Tax Cuts and Jobs Act (Tax Act) | Dividends Received Deduction for Certain Foreign Tax Credits
Income taxes
Income tax (benefit) expense			$ (102)
Tax Cuts and Jobs Act (Tax Act) | Remeasurement of Deferred Tax Assets and Liabilities
Income taxes
Income tax (benefit) expense			$ 96