Accumulated Other Comprehensive Income - Components (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ (1,898)	$ (3,193)
Other comprehensive (loss) / income before reclassifications	58	(9)
Amounts reclassified from accumulated other comprehensive income	1	4
Other comprehensive income / (loss)	59	(5)
Balance at end of period	(1,839)	(3,198)
Defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(768)	(1,464)
Other comprehensive (loss) / income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	7	15
Other comprehensive income / (loss)	7	15
Balance at end of period	(761)	(1,449)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(1,158)	(1,759)
Other comprehensive (loss) / income before reclassifications	13	(34)
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income / (loss)	13	(34)
Balance at end of period	(1,145)	(1,793)
Gains and losses on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	28	30
Other comprehensive (loss) / income before reclassifications	45	25
Amounts reclassified from accumulated other comprehensive income	(6)	(11)
Other comprehensive income / (loss)	39	14
Balance at end of period	$ 67	$ 44