Nuclear Decommissioning Trust Fund (Tables)

9 Months Ended

Sep. 30, 2018

Nuclear Decommissioning Trust Fund Disclosure [Abstract]

Summary of aggregate fair values and unrealized gains and losses (including other-than-temporary impairments) for the securities held in the nuclear decommissioning trust fund

The following table summarizes the aggregate fair values and unrealized gains and losses (including other-than-temporary impairments) for the securities held in the trust funds, as well as information about the contractual maturities of those securities.



	As of September 30, 2018							As of December 31, 2017
(In millions, except otherwise noted)	Fair Value		Unrealized Gains		Unrealized Losses		Weighted-average Maturities (In years)	Fair Value		Unrealized Gains		Unrealized Losses		Weighted-average Maturities (In years)
Cash and cash equivalents	$	21	$	—	$	—	—	$	47	$	—	$	—	—
U.S. government and federal agency obligations	41		1		1		12	43		1		—		11
Federal agency mortgage-backed securities	88		—		3		23	82		1		1		23
Commercial mortgage-backed securities	19		—		1		22	14		—		—		20
Corporate debt securities	112		1		2		10	99		2		1		11
Equity securities	434		296		—		—	402		272		—		—
Foreign government fixed income securities	4		—		—		9	5		—		—		9
Total	$	719	$	298	$	7		$	692	$	276	$	2

Summary of proceeds from sales of available-for-sale securities and the related realized gains and losses

The following table summarizes proceeds from sales of available-for-sale securities and the related realized gains and losses from these sales. The cost of securities sold is determined on the specific identification method.



	Nine months ended September 30,
	2018		2017
	(In millions)
Realized gains	$	8	$	8
Realized losses	8		6
Proceeds from sale of securities	$	398	$	382