Supplemental Financial Information - Amounts Reclassified out of AOCI (Details) - Reclassification out of Accumulated Other Comprehensive Income - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 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]	$ 13	$ 12
Tax effect		(3)	(3)
Recognized within net income, net of taxes		10	9
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)
Tax effect		0	0
Recognized within net income, net of taxes		$ 0	$ (1)

[1] Detailed in Note 6.