Early Plant Retirements Early Plant Retirements (Details) - Power [Member] - USD ($) $ in Millions		5 Months Ended	12 Months Ended
		May 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Total Pre-Tax Restructuring Costs			$ 686
Energy Costs [Member]
Restructuring Cost and Reserve [Line Items]
Coal Inventory Lower of Cost or Market Adjustments and Capacity Penalties			62
Operation and Maintenance Expense [Member]
Restructuring Cost and Reserve [Line Items]
Materials and Supplies Obsolescence			31
Write-down of Construction Work in Progress			14
Other	[1]		8
Depreciation And Amortization [Domain]
Restructuring Cost and Reserve [Line Items]
Depreciation, including Asset Retirement Costs			$ 571
Subsequent Event [Member] | Depreciation And Amortization [Domain]
Restructuring Cost and Reserve [Line Items]
Depreciation, including Asset Retirement Costs		$ 958

[1] Includes severance and miscellaneous costs. Power recorded $7 million of severance expense which it expects to pay in 2017.