Equity, Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gains (losses) reclassified out of accumulated other comprehensive income (loss)
Net of tax		$ (32)	$ (12)	$ (7)
Net Actuarial Gain (Loss) [Member]
Amortization of items related to defined benefit pension plans:
Reclassification from accumulated other comprehensive income (loss), current period, before tax	[1]	(63)	(50)	(48)
Tax benefit		14	18	18
Gains (losses) reclassified out of accumulated other comprehensive income (loss)
Net of tax		(49)	(32)	(30)
Prior Service (Cost) Credit [Member]
Amortization of items related to defined benefit pension plans:
Reclassification from accumulated other comprehensive income (loss), current period, before tax	[1]	29	36	36
Tax benefit		(7)	(13)	(13)
Gains (losses) reclassified out of accumulated other comprehensive income (loss)
Net of tax		22	23	23
Curtailment and Settlement Loss [Member]
Amortization of items related to defined benefit pension plans:
Reclassification from accumulated other comprehensive income (loss), current period, before tax	[1]	(7)	(4)	0
Tax benefit		2	1
Gains (losses) reclassified out of accumulated other comprehensive income (loss)
Net of tax		(5)	(3)
Net Gain (Loss) on Pension and Other Postretirement Benefits [Member]
Amortization of items related to defined benefit pension plans:
Reclassification from accumulated other comprehensive income (loss), current period, before tax		(41)	(18)	(12)
Tax benefit		$ 9	$ 6	$ 5

[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost (credit), as discussed in Note 13.