Supplemental Financial Information - Amounts Reclassified out of AOCI (Details) - Reclassification out of Accumulated Other Comprehensive Income - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net actuarial losses of defined benefit plans
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassified from other comprehensive income (loss), before tax	[1]	$ 15	$ 11	$ 28	$ 23
Tax effect		(4)	(2)	(7)	(5)
Recognized within net income, net of taxes		11	9	21	18
Prior service credit of defined benefit plans
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassified from other comprehensive income (loss), before tax	[1]	0	(1)	0	(2)
Tax effect		0	0	0	0
Recognized within net income, net of taxes		$ 0	$ (1)	$ 0	$ (2)

[1] Detailed in Note 6.