Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 3,577
Other comprehensive income:
Total Other comprehensive income (loss), net of tax	2	$ (40)
Ending balance	3,662
Accumulated other comprehensive loss
Other comprehensive income:
Total Other comprehensive income (loss), net of tax	2	(40)
Ending balance	(1,941)	(3,369)
Pension and other postretirement benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(980)	(2,732)
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	37	1
Tax expense	(8)	0
Total Other comprehensive income (loss) before reclassifications, net of tax	29	1
Net amount reclassified to earnings	16	43
Tax expense	(3)	(7)
Amount reclassified from Accumulated other comprehensive loss, net of tax	13	36
Total Other comprehensive income (loss), net of tax	42	37
Ending balance	(938)	(2,695)
Foreign currency translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(966)	(596)
Other comprehensive income:
Total Other comprehensive income (loss) before reclassifications, net of tax	(44)	(79)
Amount reclassified from Accumulated other comprehensive loss, net of tax	0	14
Total Other comprehensive income (loss), net of tax	(44)	(65)
Ending balance	(1,010)	(661)
Debt securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0	0
Other comprehensive income:
Total Other comprehensive income (loss), net of tax	0	1
Ending balance	0	1
Cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	3	(1)
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	8	(11)
Tax expense	(2)	(1)
Total Other comprehensive income (loss) before reclassifications, net of tax	6	(12)
Net amount reclassified to earnings	(3)	(1)
Tax expense	1	0
Amount reclassified from Accumulated other comprehensive loss, net of tax	(2)	(1)
Total Other comprehensive income (loss), net of tax	4	(13)
Ending balance	$ 7	$ (14)