Fair Value of Financial Assets and Liabilities - Non-Derivative Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021		Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Gain on Securities	$ 1,000		$ 981
Unrealized Loss on Securities	8		5
Nuclear Decommissioning Fund [Abstract]
Miscellaneous investments	56		53
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	3
Due in 1 to 5 Years	133
Due in 5 to 10 Years	202
Due after 10 Years	248
Total	586
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost
Nuclear Decommissioning Fund [Abstract]
Total	1,833	[1]	1,801	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Cash equivalents
Nuclear Decommissioning Fund [Abstract]
Cash equivalents	32	[1]	40	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Commingled Funds [Member]
Nuclear Decommissioning Fund [Abstract]
Commingled funds	795	[1]	787	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Debt Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Debt securities	562	[1]	528	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Equity Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Equity securities	444	[1]	446	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value
Nuclear Decommissioning Fund [Abstract]
NAV	1,052	[1]	1,041	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Cash equivalents
Nuclear Decommissioning Fund [Abstract]
Cash equivalents	32	[1]	40	[2]
NAV	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Commingled Funds [Member]
Nuclear Decommissioning Fund [Abstract]
Commingled funds	1,052	[1]	1,041	[2]
NAV	1,052	[1]	1,041	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Debt Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Debt securities	586	[1]	585	[2]
NAV	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Equity Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Equity securities	1,155	[1]	1,111	[2]
NAV	0	[1]	0	[2]
Total	2,825	[1]	2,777	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1
Nuclear Decommissioning Fund [Abstract]
Total	1,185	[1]	1,149	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Cash equivalents
Nuclear Decommissioning Fund [Abstract]
Cash equivalents	32	[1]	40	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Commingled Funds [Member]
Nuclear Decommissioning Fund [Abstract]
Commingled funds	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Debt Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Debt securities	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Equity Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Equity securities	1,153	[1]	1,109	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2
Nuclear Decommissioning Fund [Abstract]
Total	575	[1]	574	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Cash equivalents
Nuclear Decommissioning Fund [Abstract]
Cash equivalents	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Commingled Funds [Member]
Nuclear Decommissioning Fund [Abstract]
Commingled funds	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Debt Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Debt securities	573	[1]	572	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Equity Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Equity securities	2	[1]	2	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3
Nuclear Decommissioning Fund [Abstract]
Total	13	[1]	13	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Cash equivalents
Nuclear Decommissioning Fund [Abstract]
Cash equivalents	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Commingled Funds [Member]
Nuclear Decommissioning Fund [Abstract]
Commingled funds	0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Debt Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Debt securities	13	[1]	13	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Equity Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Equity securities	$ 0	[1]	$ 0	[2]

[1] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheets, which also includes $56 million of rabbi trust assets and miscellaneous investments.

[2] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheets, which also includes $53 million of rabbi trust assets and miscellaneous investments.