SONGS NDT 1 (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
		Mar. 31, 2016		Mar. 31, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 662			$ 660
Gross Unrealized Gains		433			423
Gross Unrealized Loss		(13)			(20)
Estimated fair value		1,082			1,063
Proceeds from sales	[1]	93		$ 94
Gross realized gains		3		2
Gross realized losses		(8)		$ (4)
Total Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost		439			431
Gross Unrealized Gains		20			11
Gross Unrealized Loss		(8)			(13)
Estimated fair value		451			429
Debt Securities Issued By The U.S. Treasury And Other U.S. Government Corporations And Agencies
Schedule of Available-for-sale Securities [Line Items]
Cost		101	[2]		89
Gross Unrealized Gains		4	[2]		2
Gross Unrealized Loss		0	[2]		0
Estimated fair value		105	[2]		91
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost		146	[3]		148
Gross Unrealized Gains		10	[3]		8
Gross Unrealized Loss		0	[3]		0
Estimated fair value		156	[3]		156
Other Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost		192	[3]		194
Gross Unrealized Gains		6	[3]		1
Gross Unrealized Loss		(8)	[3]		(13)
Estimated fair value		190	[3]		182
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost		214			214
Gross Unrealized Gains		413			412
Gross Unrealized Loss		(4)			(7)
Estimated fair value		623			619
Cash And Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Cost		9			15
Gross Unrealized Gains		0			0
Gross Unrealized Loss		(1)			0
Estimated fair value		$ 8			$ 15

[1] Excludes securities that are held to maturity.

[2] Maturity dates are 2016-2065.

[3] Maturity dates are 2016-2115.