Employee Benefit Plans - Change in Level 3 Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of plan assets at beginning of year	$ 129	$ 107
Fair value of assets at end of year	148	129
Level 3
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of plan assets at beginning of year	5	4
Unrealized gain on asset still held	4	1
Fair value of assets at end of year	$ 9	$ 5