Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ (1,551)		$ (1,372)		$ (1,593)		$ (1,356)
Other comprehensive income/(loss) before reclassifications	(7)		3		(16)		(50)
Amounts reclassified from accumulated other comprehensive income/(loss)	25		18		76		55
Net to-date other comprehensive income/(loss), net of taxes	18	[1]	21	[1]	60	[2]	5	[2]
Balance at September 30	(1,533)		(1,351)		(1,533)		(1,351)
Deferred taxes activity other comprehensive income/(loss)	(8)		(6)		(26)		(18)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(1,332)		(1,110)		(1,381)		(1,150)
Other comprehensive income/(loss) before reclassifications	(1)				(3)		3
Amounts reclassified from accumulated other comprehensive income/(loss)	25		18		76		55
Net to-date other comprehensive income/(loss), net of taxes	24		18		73		58
Balance at September 30	(1,308)		(1,092)		(1,308)		(1,092)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(219)		(262)		(212)		(206)
Other comprehensive income/(loss) before reclassifications	(6)		3		(13)		(53)
Net to-date other comprehensive income/(loss), net of taxes	(6)		3		(13)		(53)
Balance at September 30	$ (225)		$ (259)		$ (225)		$ (259)

[1] Net of deferred taxes of ($8) million and ($6) million during the three months ended September 30, 2021 and 2020, respectively.

[2] Net of deferred taxes of ($26) million and ($18) million during the nine months ended September 30, 2021 and 2020, respectively.