Benefit Plans - Rollforward of level 3 plan assets (Details) - Pension benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets
Fair value of plan assets, beginning of year	$ 6,987	$ 6,192
Fair value of plan assets, end of year	6,525	6,987	$ 6,192
Significant unobservable inputs (Level 3)
Change in plan assets
Fair value of plan assets, beginning of year	2	0	5
Actual return on plan assets: Relating to assets sold during the period	0	0	0
Actual return on plan assets: Relating to assets still held at the reporting date	0	0	0
Purchases, sales and settlements, net	0	2	(5)
Net transfers in (out) of Level 3	0	0	0
Fair value of plan assets, end of year	2	2	0
Significant unobservable inputs (Level 3) | Equity securities
Change in plan assets
Fair value of plan assets, beginning of year	0
Actual return on plan assets: Relating to assets sold during the period	0
Actual return on plan assets: Relating to assets still held at the reporting date	0
Purchases, sales and settlements, net	2
Net transfers in (out) of Level 3	0
Fair value of plan assets, end of year	2	0
Significant unobservable inputs (Level 3) | Corporate
Change in plan assets
Fair value of plan assets, beginning of year	2	0	5
Actual return on plan assets: Relating to assets sold during the period	0	0	0
Actual return on plan assets: Relating to assets still held at the reporting date	0	0	0
Purchases, sales and settlements, net	(2)	2	(5)
Net transfers in (out) of Level 3	0	0	0
Fair value of plan assets, end of year	$ 0	$ 2	$ 0