Accumulated Other Comprehensive Income (Loss) - After-tax Changes by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (3,996)	$ (3,495)	$ (3,964)	$ (3,422)
Amounts arising during the period	(274)	(173)	(346)	(310)
Reclassifications from AOCI	(2)	20	38	84
Net OCI during the period	(276)	(153)	(308)	(226)
Balance at end of period	(4,272)	(3,648)	(4,272)	(3,648)
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,616)	(1,223)	(1,533)	(1,089)
Amounts arising during the period	(285)	(187)	(368)	(321)
Reclassifications from AOCI	0	0	0	0
Net OCI during the period	(285)	(187)	(368)	(321)
Balance at end of period	(1,901)	(1,410)	(1,901)	(1,410)
Unrealized gains (losses) on qualifying derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	6	(21)	(7)	(13)
Amounts arising during the period	16	22	32	21
Reclassifications from AOCI	(22)	(14)	(25)	(21)
Net OCI during the period	(6)	8	7	0
Balance at end of period	0	(13)	0	(13)
Defined benefit plans Prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(18)	(7)	(19)	(7)
Amounts arising during the period	0	0	0	(1)
Reclassifications from AOCI	0	0	1	1
Net OCI during the period	0	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	(2,368)	(2,244)	(2,405)	(2,313)
Amounts arising during the period	(5)	(8)	(10)	(9)
Reclassifications from AOCI	20	34	62	104
Net OCI during the period	15	26	52	95
Balance at end of period	$ (2,353)	$ (2,218)	$ (2,353)	$ (2,218)