Employee Benefits - Change in Plan Assets Measured at Fair Value (Details) - Combined Pension Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Change in plan assets
Fair value of plan assets at beginning of year	$ 10,546	$ 10,493
Fair value of plan assets at end of year	8,531	10,546
Level 3
Change in plan assets
Fair value of plan assets at beginning of year	8	22
Acquisitions (dispositions)		(16)
Actual return on plan assets	3	2
Fair value of plan assets at end of year	11	8
Level 3 | High Yield Bonds
Change in plan assets
Fair value of plan assets at beginning of year	6	5
Acquisitions (dispositions)		1
Actual return on plan assets	0	0
Fair value of plan assets at end of year	6	6
Level 3 | U.S. Stocks
Change in plan assets
Fair value of plan assets at beginning of year	2	1
Acquisitions (dispositions)		0
Actual return on plan assets	3	1
Fair value of plan assets at end of year	5	2
Level 3 | Private Debt
Change in plan assets
Fair value of plan assets at beginning of year	0	16
Acquisitions (dispositions)		(17)
Actual return on plan assets	0	1
Fair value of plan assets at end of year	$ 0	$ 0