Accumulated Other Comprehensive Income (Loss) - After-tax Changes by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (4,366)	$ (3,647)	$ (4,358)	$ (3,964)
Amounts arising during the period	(264)	(344)	(317)	(72)
Reclassifications from AOCI	28	(5)	73	40
Net OCI during the period	(236)	(349)	(244)	(32)
Balance at end of period	(4,602)	(3,996)	(4,602)	(3,996)
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,486)	(1,239)	(1,425)	(1,533)
Amounts arising during the period	(291)	(377)	(352)	(83)
Reclassifications from AOCI	0	0	0	0
Net OCI during the period	(291)	(377)	(352)	(83)
Balance at end of period	(1,777)	(1,616)	(1,777)	(1,616)
Unrealized gains (losses) on qualifying derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	0	(2)	(5)	(7)
Amounts arising during the period	28	35	36	16
Reclassifications from AOCI	(20)	(27)	(23)	(3)
Net OCI during the period	8	8	13	13
Balance at end of period	8	6	8	6
Defined benefit plans Prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(17)	(19)	(18)	(19)
Amounts arising during the period	0	0	0	0
Reclassifications from AOCI	1	1	2	1
Net OCI during the period	1	1	2	1
Balance at end of period	(16)	(18)	(16)	(18)
Defined benefit plans Actuarial gain (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(2,863)	(2,387)	(2,910)	(2,405)
Amounts arising during the period	(1)	(2)	(1)	(5)
Reclassifications from AOCI	47	21	94	42
Net OCI during the period	46	19	93	37
Balance at end of period	$ (2,817)	$ (2,368)	$ (2,817)	$ (2,368)