Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Components of Net Periodic Benefit Expense and Other Postretirement Expense (Income):
Service cost	$ 13	$ 11	$ 39	$ 34
Interest cost	8	8	24	23
Expected return on plan assets	(7)	(6)	(21)	(20)
Recognized net actuarial loss	5	4	16	14
Recognized curtailment loss and settlement cost	0	0	0	5
Net Periodic Benefit Expense (Income)	19	17	58	56
Other Postretirement Benefits
Components of Net Periodic Benefit Expense and Other Postretirement Expense (Income):
Service cost	1	0	2	2
Interest cost	1	1	2	2
Amortization of prior service credit	(8)	(8)	(25)	(26)
Recognized net actuarial loss	0	1	2	3
Net Periodic Benefit Expense (Income)	$ (6)	$ (6)	$ (19)	$ (19)