Income Taxes - Tax Effected Operating Loss, Capital Loss, and Tax Credit Carryovers (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Federal jurisdiction
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers	$ 7
Federal jurisdiction | Maximum
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers, expiration date	20 years
Federal jurisdiction | Minimum
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers, expiration date	15 years
State jurisdiction
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers	$ 12
State jurisdiction | Maximum
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers, expiration date	10 years
State jurisdiction | Minimum
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers, expiration date	5 years
International jurisdiction
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers	$ 70
International jurisdiction | Maximum
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers, expiration date	3 years
International jurisdiction | Minimum
Tax effected operating loss, capital loss, and tax credit carryovers
Tax effected operating loss, capital loss, and tax credit carryovers, expiration date	1 year