Employee Benefits - Change in Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets
Return on plan assets	$ 422	$ 1,200
Combined Pension Plan
Change in plan assets
Fair value of plan assets at beginning of year	10,546	10,493	$ 10,033
Return on plan assets	422	1,210	1,575
Benefits paid from plan assets	(766)	(1,157)	(1,115)
Settlement payments and annuity purchase	(1,671)	0	0
Fair value of plan assets at end of year	$ 8,531	$ 10,546	$ 10,493