Benefit Plans - Cash flows (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension benefits
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	$ 19,000,000
Employer contribution	14,000,000	$ 24,000,000
Postretirement benefits
Components of net periodic cost
Defined benefit pension plans, estimated employer contributions in next fiscal year	0
Employer contribution	26,000,000	26,000,000
Participant contributions	$ 16,000,000	$ 16,000,000