Income Taxes Level 4 AMT credit and foreign tax credit carryover (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	$ 49	$ 56
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	650	640
Deferred Tax Assets, Tax Credit Carryforwards, General Business	90	99
No expiration tax year [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	$ 650
Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2021
Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2024
Expiring within Tax Years 2019 to 2024 [Member] [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	$ 49
Expiring Tax Year 2036 [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2036
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Deferred Tax Asset	$ 49	$ 56