Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Limit on NOL Carryforward Deduction	80.00%
Valuation allowance	$ 653	$ 964
Change in valuation allowance	311	(1)	$ 9
Accrued interest and penalties related to unrecognized tax	1	1
Unrecognized Tax Benefits, Interest on Income Taxes Expense	0	0	(6)
Unrecognized tax benefits	37	36	45	$ 62
Deferred Tax Asset, Operating Loss Carryforward
Income Tax Contingency [Line Items]
Valuation allowance	1,007	1,318
Change in valuation allowance		(6)	14
Deferred Tax Asset, Capital Loss Carryforward
Income Tax Contingency [Line Items]
Valuation allowance	(354)	(354)
Change in valuation allowance		5	$ (5)
Valuation allowance on deferred tax assets
Income Tax Contingency [Line Items]
Valuation allowance	$ 653	$ 964