Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		$ 7,592
Total income tax expense		33		$ 45		$ 80
Accumulated other comprehensive loss at end of period		8,444		7,592
Gains and Losses on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		(23)		(24)
Amortization of net actuarial income (loss)		(1)		0
Net current period other comprehensive income (loss)		2		1
Accumulated other comprehensive loss at end of period		(21)		(23)		(24)
Gains and Losses on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total income tax expense		0		0
Reclassification from AOCI, Current Period, Tax		0		0
Gains and Losses on Cash Flow Hedges | Interest Rate Swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amortization of net actuarial income (loss)		(1)	[1]	(1)	[2]
Defined Benefit Pension and Postretirement Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		(1)		(3)
Amortization of net actuarial income (loss)	[3]	0		(2)
Net current period other comprehensive income (loss)		0		2
Accumulated other comprehensive loss at end of period		(1)		(1)		(3)
Defined Benefit Pension and Postretirement Items | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total income tax expense		0		0
Reclassification from AOCI, Current Period, Tax		0		1
Defined Benefit Pension and Postretirement Items | Interest Rate Swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amortization of net actuarial income (loss)		0		0
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		(24)		(27)
Amortization of net actuarial income (loss)		(1)		(2)
Net current period other comprehensive income (loss)		2		3
Accumulated other comprehensive loss at end of period		(22)		(24)		$ (27)
Total | Interest Rate Swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amortization of net actuarial income (loss)		$ (1)		$ (1)

[1] Included in interest charges.

[2] Included in interest charges.

[3] Included in the computation of net periodic pension and postretirement benefit costs. See Note 9 for further information.