Early Nuclear Plant Retirements Early Plant Retirement Pretax Expense (Details) - USD ($) $ in Millions		3 Months Ended					12 Months Ended
		Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016
Depreciation	[1]	$ 754				$ 606
Other Cost and Expense, Operating		2,460				2,835
Other, net		$ 283				$ 114
Nuclear Plant [Member]
Nuclear Fuel Amortization			$ 23	$ 28	$ 9		$ 60
Depreciation			253	344	115		712
Other Cost and Expense, Operating			(120)	5	141		26
Accretion Expense, Including Asset Retirement Obligations			0	2	0		2
Other, net			(31)	(41)	(14)		(86)
Other Expenses			$ 125	$ 338	$ 251		714
Facility Closing [Member]
Other Expenses							$ 714

[1] (a)Included in Depreciation and amortization on the Registrants' Consolidated Statements of Operations and Comprehensive Income.