Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension benefits
Components of net periodic cost
Service cost	$ 29	$ 28	$ 85	$ 85
Interest cost	60	66	181	198
Expected return on plan assets	(105)	(102)	(316)	(306)
Amortization of prior service credit	(14)	(14)	(42)	(42)
Amortization of net actuarial loss (gain)	43	48	132	142
Settlement loss	68	94	82	110
Net periodic postretirement credit	81	120	122	187
Postretirement benefits
Components of net periodic cost
Service cost	2	2	6	6
Interest cost	3	4	10	11
Amortization of prior service credit	(5)	(6)	(16)	(18)
Amortization of net actuarial loss (gain)	(6)	(6)	(17)	(18)
Net periodic postretirement credit	(6)	(6)	$ (17)	$ (19)
Corporate and Other | Pension benefits
Components of net periodic cost
Settlement loss	$ 61	$ 86