Income Taxes (Operating Loss Carryforwards Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Valuation Allowance	$ 489
Operating Loss Carryforwards, Additional Valuation Allowance	2
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss and credit carryforwards	610
Operating loss carryforwards expected to be utilized	136
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss and credit carryforwards	6,300
Operating loss carryforwards expected to be utilized	$ 16
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2018
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037