Non-Derivative Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020		Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Gain on Securities	$ 454		$ 706
Unrealized Loss on Securities	88		6
Nuclear decommissinoning fund [Abstract]
Equity investments in unconsolidated subsidiaries	158		155
Miscellaneous investments	129		136
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Due in one year or less	11
Due in 1 to 5 years	81
Due in 5 to 10 years	205
Due after 10 years	204
Total	501
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost
Nuclear decommissinoning fund [Abstract]
Decommissioning Fund Investments	1,776	[1]	1,740	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Cash equivalents
Nuclear decommissinoning fund [Abstract]
Cash equivalents	71	[1]	33	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Commingled funds
Nuclear decommissinoning fund [Abstract]
Commingled funds	756	[1]	733	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Debt securities
Nuclear decommissinoning fund [Abstract]
Debt securities	514	[1]	489	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Equity securities
Nuclear decommissinoning fund [Abstract]
Equity securities	435	[1]	485	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value
Nuclear decommissinoning fund [Abstract]
Alternative investment	843	[1]	935	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Cash equivalents
Nuclear decommissinoning fund [Abstract]
Cash equivalents	71	[1]	33	[2]
Alternative investment	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Commingled funds
Nuclear decommissinoning fund [Abstract]
Commingled funds	843	[1]	935	[2]
Alternative investment	843	[1]	935	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Debt securities
Nuclear decommissinoning fund [Abstract]
Debt securities	501	[1]	508	[2]
Alternative investment	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Equity securities
Nuclear decommissinoning fund [Abstract]
Equity securities	727	[1]	964	[2]
Alternative investment	0	[1]	0	[2]
Decommissioning Fund Investments	2,142	[1]	2,440	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1
Nuclear decommissinoning fund [Abstract]
Decommissioning Fund Investments	797	[1]	995	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Cash equivalents
Nuclear decommissinoning fund [Abstract]
Cash equivalents	71	[1]	33	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Commingled funds
Nuclear decommissinoning fund [Abstract]
Commingled funds	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Debt securities
Nuclear decommissinoning fund [Abstract]
Debt securities	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Equity securities
Nuclear decommissinoning fund [Abstract]
Equity securities	726	[1]	962	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2
Nuclear decommissinoning fund [Abstract]
Decommissioning Fund Investments	489	[1]	497	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Cash equivalents
Nuclear decommissinoning fund [Abstract]
Cash equivalents	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Commingled funds
Nuclear decommissinoning fund [Abstract]
Commingled funds	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Debt securities
Nuclear decommissinoning fund [Abstract]
Debt securities	488	[1]	495	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Equity securities
Nuclear decommissinoning fund [Abstract]
Equity securities	1	[1]	2	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3
Nuclear decommissinoning fund [Abstract]
Decommissioning Fund Investments	13	[1]	13	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Cash equivalents
Nuclear decommissinoning fund [Abstract]
Cash equivalents	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Commingled funds
Nuclear decommissinoning fund [Abstract]
Commingled funds	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Debt securities
Nuclear decommissinoning fund [Abstract]
Debt securities	13	[1]	13	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Equity securities
Nuclear decommissinoning fund [Abstract]
Equity securities	$ 0	[1]	$ 0	[2]

[1] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $158 million of equity investments in unconsolidated subsidiaries and $129 million of rabbi trust assets and miscellaneous investments.

[2] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $155 million of equity investments in unconsolidated subsidiaries and $136 million of rabbi trust assets and miscellaneous investments.