Income Taxes - Deferred Tax Assets and Valuation Allowances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Valuation Allowance [Line Items]
Deferred tax assets related to operating loss carryovers	$ 1,261	$ 1,249
Deferred tax assets related to general business, alternative minimum and foreign tax credits	258	260
Deferred tax assets related to capital losses		17
Valuation allowance related to deferred tax assets	155	178
Change in valuation allowance	23
Net Operating Loss Carryovers Tax Credits and Capital Losses
Valuation Allowance [Line Items]
Valuation allowance related to deferred tax assets	117	$ 140
Capital Loss Carryforward
Valuation Allowance [Line Items]
Change in valuation allowance	$ 18