Benefit Plans - Cash flows narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension benefits
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	$ 25,000,000
Employer contribution	27,000,000	$ 16,000,000
Postretirement benefits
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	0
Employer contribution	24,000,000	22,000,000
Participant contributions	15,000,000	$ 13,000,000
Other Pension Plan
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	$ 4,000,000