Pension and Other Postretirement Benefits, Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Net loss (gain)	$ 41
Prior service credit	(2)
Total amount expected to be amortized	39
Pension Plans [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Net loss (gain)	(3)	$ 200	$ 179
Prior service (cost) credit	(13)	(4)	15
Amortization of net (loss) gain	(74)	(61)	(52)
Amortization of prior service (cost) credit	2	(1)	0
Total recognized in other comprehensive income (loss)	(88)	134	142
Total recognized in net periodic benefit cost and other comprehensive income (loss)	8	244	239
Net loss (gain)	44
Prior service credit	(2)
Total amount expected to be amortized	42
Postretirement Benefit Plans [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Net loss (gain)	(2)	(17)	(4)
Prior service (cost) credit	0	0	(2)
Amortization of net (loss) gain	3	2	2
Amortization of prior service (cost) credit	1	1	2
Total recognized in other comprehensive income (loss)	2	(14)	(2)
Total recognized in net periodic benefit cost and other comprehensive income (loss)	0	$ (14)	$ (2)
Net loss (gain)	(3)
Prior service credit	0
Total amount expected to be amortized	$ (3)