Fair Value Measurements - Recurring Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Liabilities
Restricted cash	$ 27	$ 49
Recurring
Assets
Fair value, assets	616	1,837
Liabilities
Fair value, liabilities	0	(1)
Net assets (liabilities)	616	1,836
Recurring | FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	0	(1)
Recurring | FTRs | Derivative Assets
Assets
Fair value, assets	1	9
Recurring | Equity securities
Assets
Fair value, assets	2	2
Recurring | U.S. state debt securities
Assets
Fair value, assets	258	273
Recurring | Cash, cash equivalents and restricted cash
Assets
Fair value, assets	310	1,511
Recurring | Other
Assets
Fair value, assets	45	42
Recurring | Level 1
Assets
Fair value, assets	312	1,513
Liabilities
Fair value, liabilities	0	0
Net assets (liabilities)	312	1,513
Recurring | Level 1 | FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Recurring | Level 1 | FTRs | Derivative Assets
Assets
Fair value, assets	0	0
Recurring | Level 1 | Equity securities
Assets
Fair value, assets	2	2
Recurring | Level 1 | U.S. state debt securities
Assets
Fair value, assets	0	0
Recurring | Level 1 | Cash, cash equivalents and restricted cash
Assets
Fair value, assets	310	1,511
Recurring | Level 1 | Other
Assets
Fair value, assets	0	0
Recurring | Level 2
Assets
Fair value, assets	303	315
Liabilities
Fair value, liabilities	0	0
Net assets (liabilities)	303	315
Recurring | Level 2 | FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Recurring | Level 2 | FTRs | Derivative Assets
Assets
Fair value, assets	0	0
Recurring | Level 2 | Equity securities
Assets
Fair value, assets	0	0
Recurring | Level 2 | U.S. state debt securities
Assets
Fair value, assets	258	273
Recurring | Level 2 | Cash, cash equivalents and restricted cash
Assets
Fair value, assets	0	0
Recurring | Level 2 | Other
Assets
Fair value, assets	45	42
Recurring | Level 3
Assets
Fair value, assets	1	9
Liabilities
Fair value, liabilities	0	(1)
Net assets (liabilities)	1	8
Recurring | Level 3 | FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	0	(1)
Recurring | Level 3 | FTRs | Derivative Assets
Assets
Fair value, assets	1	9
Recurring | Level 3 | Equity securities
Assets
Fair value, assets	0	0
Recurring | Level 3 | U.S. state debt securities
Assets
Fair value, assets	0	0
Recurring | Level 3 | Cash, cash equivalents and restricted cash
Assets
Fair value, assets	0	0
Recurring | Level 3 | Other
Assets
Fair value, assets	$ 0	$ 0