CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Comprehensive income:
Net income	$ 660	$ 588	$ 578
Pension and retiree medical benefits:
Reclassification of loss (gain) to net income, net of tax of $—, $1 and $(1), respectively	0	2	(3)
Derivative instruments:
Reclassification of loss to net income, net of tax of $—, $— and $—, respectively	2	1	2
Total other comprehensive income (loss)	2	3	(1)
Total comprehensive income	662	591	577
Defined Benefit Plan Reclassification Adjustment from AOCI, Tax	0	1	(1)
Reclassification Adjustment from AOCI on Derivatives, Tax	0	0	0
Net income	660	588	578
Reclassification of loss (gain) to net income, net of tax of $—, $1 and $(1), respectively	0	2	(3)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(2)	(1)	(2)
Total other comprehensive income (loss)	2	3	(1)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 662	$ 591	$ 577