Pension and Other Postretirement Plans - Defined Benefit Plan Assets Measured at Fair Value Using Unobservable Inputs (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	$ 401	$ 409
Actual return (loss) on plan assets:
Sold during the year	2	4
Held at year end	48	13
Purchases, sales, issuances and settlements (net)	(14)	(25)
Fair value of plan assets at end of year	$ 437	$ 401