Fair Value (Details Textuals) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Nuclear decommissioning trusts | Fixed Income Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities with no contractual maturity date	$ 82
Private Equity and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unfunded commitments related to investments classified as NAV assets	$ 183	$ 151
Minimum | Equity or debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, redemption notice period	7 days
Minimum | Private Equity and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments classified as NAV assets, general contractual durations	7 years
Maximum | Equity or debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, redemption notice period	65 days
Maximum | Private Equity and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments classified as NAV assets, general contractual durations	12 years