Accumulated Other Comprehensive Income (Loss) - After-tax Changes by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (3,647)	$ (3,279)	$ (3,964)	$ (3,422)
Amounts arising during the period	(344)	(232)	(72)	(137)
Reclassifications from AOCI	(5)	16	40	64
Net OCI during the period	(349)	(216)	(32)	(73)
Balance at end of period	(3,996)	(3,495)	(3,996)	(3,495)
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,239)	(973)	(1,533)	(1,089)
Amounts arising during the period	(377)	(250)	(83)	(134)
Reclassifications from AOCI	0	0	0	0
Net OCI during the period	(377)	(250)	(83)	(134)
Balance at end of period	(1,616)	(1,223)	(1,616)	(1,223)
Unrealized gains (losses) on qualifying derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(2)	(21)	(7)	(13)
Amounts arising during the period	35	19	16	(1)
Reclassifications from AOCI	(27)	(19)	(3)	(7)
Net OCI during the period	8	0	13	(8)
Balance at end of period	6	(21)	6	(21)
Defined benefit plans Prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(19)	(7)	(19)	(7)
Amounts arising during the period	0	(1)	0	(1)
Reclassifications from AOCI	1	1	1	1
Net OCI during the period	1	0	1	0
Balance at end of period	(18)	(7)	(18)	(7)
Defined benefit plans Actuarial gain (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(2,387)	(2,278)	(2,405)	(2,313)
Amounts arising during the period	(2)	0	(5)	(1)
Reclassifications from AOCI	21	34	42	70
Net OCI during the period	19	34	37	69
Balance at end of period	$ (2,368)	$ (2,244)	$ (2,368)	$ (2,244)