CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Comprehensive income:
Net income	$ 287	$ 238	$ 582	$ 553
Pension and retiree medical benefits:
Net pension and retiree medical gains arising during the period, net of tax of $—, $—, $— and $1, respectively	0	1	0	3
Net pension gains, tax	0	0	0	1
Reclassifications of loss to net income, net of tax of $1, $—, $1 and $—, respectively	2	0	3	1
Pension reclassification's, Tax	1	0	1	0
Derivative instruments:
Net fair value decrease, net of tax of $—, $(3), $(3) and $(5), respectively	0	(10)	(10)	(17)
Derivative fair value decrease, tax	0	(3)	(3)	(5)
Reclassification of loss to net income, net of tax of $1, $—, $1 and $—, respectively	1	1	3	2
Derivative reclassification's, tax	1	0	1	0
Other comprehensive income	3	(8)	(4)	(11)
Total comprehensive income	$ 290	$ 230	$ 578	$ 542