Income Taxes Level 4 AMT Credit and Foreign Tax Credit Carryover (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	$ 241	$ 232
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	29	40
Tax Credit Carryforward, Valuation Allowance		$ 1
Valuation Allowance, Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Valuation Allowance	$ 0
Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2022
Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2024