Pension and Other Postretirement Benefits, Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 103	$ 97	$ 94
Interest cost	143	142	135
Expected return on plan assets	(223)	(197)	(186)
Amortization of prior service cost (credits)	(2)	1	0
Amortization of net loss (gains)	74	61	52
Curtailment loss and special termination benefits	1	6	2
Net periodic benefit cost	96	110	97
Postretirement Benefit Plans [Member]
Components of net periodic benefit cost [Abstract]
Service cost	2	2	2
Interest cost	5	5	6
Expected return on plan assets	(5)	(4)	(4)
Amortization of prior service cost (credits)	(1)	(1)	(2)
Amortization of net loss (gains)	(3)	(2)	(2)
Curtailment loss and special termination benefits	0	0	0
Net periodic benefit cost	(2)	0	0
Accounting Standards Update 2017-07 [Member]
Defined Benefit Plan Disclosure [Line Items]
New accounting pronouncement or change in accounting principle, effect of change on operating income	$ 11	11	1
Accounting Standards Update 2017-07 [Member] | Pension Plans [Member]
Components of net periodic benefit cost [Abstract]
Service cost		$ 15	$ 14