Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		$ 9,742
Accumulated other comprehensive loss at end of period		9,847
Income Tax Expense (Benefit)		15	$ 17
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		(19)	(20)
Losses reclassified from net accumulated other comprehensive loss	[1]	0	0
Net current period other comprehensive loss		0	0
Accumulated other comprehensive loss at end of period		(19)	(20)
Defined Benefit and Postretirement Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		(1)	(2)
Losses reclassified from net accumulated other comprehensive loss	[1]	0	(1)
Net current period other comprehensive loss		0	1
Accumulated other comprehensive loss at end of period		(1)	(1)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period		(20)	(22)
Losses reclassified from net accumulated other comprehensive loss	[1]	0	(1)
Net current period other comprehensive loss		0	1
Accumulated other comprehensive loss at end of period		$ (20)	$ (21)

[1] Included in the computation of net periodic pension and postretirement benefit costs. See Note 8 for further information.