Accumulated Other Comprehensive Income (Loss) - After-tax Changes by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (4,358)	$ (3,964)
Amounts arising during the period	(53)	272
Reclassifications from AOCI	45	45
Net OCI during the period	(8)	317
Balance at end of period	(4,366)	(3,647)
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,425)	(1,533)
Amounts arising during the period	(61)	294
Reclassifications from AOCI	0	0
Net OCI during the period	(61)	294
Balance at end of period	(1,486)	(1,239)
Unrealized gains (losses) on qualifying derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(5)	(7)
Amounts arising during the period	8	(19)
Reclassifications from AOCI	(3)	24
Net OCI during the period	5	5
Balance at end of period	0	(2)
Defined benefit plans Prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(18)	(19)
Amounts arising during the period	0	0
Reclassifications from AOCI	1	0
Net OCI during the period	1	0
Balance at end of period	(17)	(19)
Defined benefit plans Actuarial gain (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(2,910)	(2,405)
Amounts arising during the period	0	(3)
Reclassifications from AOCI	47	21
Net OCI during the period	47	18
Balance at end of period	$ (2,863)	$ (2,387)