Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Abstract]
Operating Loss Carryforwards, Valuation Allowance	$ 504	$ 504
Unrecognized benefit that would affect the effective tax rate	7	7
Amount of interest and penalties included in liabilities for uncertain tax positions	4	$ 4
Effective Income Tax Rate, Continuing Operations		1.50%	15.80%	6.10%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent			(1.10%)
U.S. federal corporate tax rate		21.00%	35.00%	35.00%
Income Tax Expense (Benefit)		$ (11)	$ (449)	$ (104)
Federal and state deferred tax assets	1,211	1,211	1,023
Deferred Tax Assets, Valuation Allowance	701	701	489
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit)		32
Cash Paid for Income Taxes, Net of Refunds Received [Abstract]
Income tax refund		19		16
Income tax paid, net		$ 19	$ (4)	$ 16
Adjusted for the Expense Related to Income Attributable to Noncontrolling Interest [Member]
Income Tax Contingency [Abstract]
Effective Income Tax Rate, Continuing Operations		1.40%	15.50%	5.70%
Tax Reform Act Release of Certain State Valuation Allowances [Member]
Income Tax Contingency [Abstract]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent		2.50%
Income Tax Expense (Benefit)	18
Interest Limitations Under IRC Section 163(j) [Member]
Income Tax Contingency [Abstract]
Federal and state deferred tax assets	144	$ 144
Deferred Tax Assets, Valuation Allowance	196	196
Expected to be Deductible as Interest Expense [Member]
Income Tax Contingency [Abstract]
Federal and state deferred tax assets	$ 101	$ 101
Scenario, Plan [Member]
Income Tax Contingency [Abstract]
U.S. federal corporate tax rate		21.00%