Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions			12 Months Ended
		Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at January 1			$ (1,415)	$ (1,141)
Other comprehensive income/(loss) before reclassifications			(69)	(37)
Amounts reclassified from accumulated other comprehensive income/(loss)	[1]		36	63
OPEB Plan amendment (Note 6)		$ 92	92
Net year-to-date other comprehensive income/(loss), net of taxes	[2]		59	26	$ 131
Reclassification due to ASU 2018-02 adoption	[3]			(300)
Balance at December 31			(1,356)	(1,415)	(1,141)
Deferred taxes activity other comprehensive income/(loss)			(15)	(22)	(61)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at January 1			(1,192)	(1,029)
Other comprehensive income/(loss) before reclassifications			(86)	(1)
Amounts reclassified from accumulated other comprehensive income/(loss)	[1]		36	63
OPEB Plan amendment (Note 6)			92
Net year-to-date other comprehensive income/(loss), net of taxes			42	62
Reclassification due to ASU 2018-02 adoption	[3]			(225)
Balance at December 31			(1,150)	(1,192)	(1,029)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at January 1			(223)	(112)
Other comprehensive income/(loss) before reclassifications			17	(36)
Amounts reclassified from accumulated other comprehensive income/(loss)	[1]
Net year-to-date other comprehensive income/(loss), net of taxes			17	(36)
Reclassification due to ASU 2018-02 adoption	[3]			(75)
Balance at December 31			$ (206)	$ (223)	$ (112)

[1] The accumulated other comprehensive income/(loss) reclassification components are 1) prior service cost/(credit) and 2) net actuarial loss which are both included in the computation of net periodic pension cost. See Note 6 Retirement Plans for additional details.

[2] Net of deferred taxes of ($15) million, ($22) million, and ($61) million during 2019, 2018, and 2017, respectively.

[3] ASU 2018-02 is the Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows entities the option to reclassify from accumulated other comprehensive income to retained earnings the income tax effects that remain stranded in AOCI resulting from the application of the Tax Cuts and Jobs Act.