Benefit Plans - Cash flows narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension benefits
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	$ 24
Employer contribution	18	$ 27
Postretirement benefits
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	0
Employer contribution	23	24
Participant contributions	14	$ 15
Other Pension Plan
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	$ 4