Defined Benefit Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Amortization:
Net settlement loss	$ (2)	$ 8	$ (9)	$ 11
Estimated future contributions over the remainder of the current year	6		6
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	4	14	13
Interest cost	3	7	17	20
Expected return on plan assets	(3)	(9)	(19)	(26)
Amortization:
– prior service credit	(1)	(2)	(5)	(7)
– actuarial loss	2	3	6	9
Net settlement loss	0		2	16
Net periodic benefit cost	6	13	15	25
Payment for other postretirement benefit plans	20		20
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	1
Interest cost	1	2	3	6
Expected return on plan assets	0	0	0	0
Amortization:
– prior service credit	(5)	(2)	(14)	(6)
– actuarial loss	1	0	1	1
Net settlement loss	0	0	0	0
Net periodic benefit cost	$ (3)	$ 0	(10)	$ 2
Payment for other postretirement benefits			17
Funded Plan
Amortization:
Payment for pension benefits			35
Unfunded Plan
Amortization:
Payment for pension benefits			$ 4