Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 45,338
Other comprehensive income, net of tax	$ 243	$ 108	390	$ 850
Less: Net translation of foreign currencies attributable to noncontrolling interests	(4)	1	(10)	(3)
Shareholders other comprehensive income (loss), net of tax	247	107	400	853
Ending balance	48,032		48,032
Securities and Derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,256	803	975	18
Other comprehensive income (loss) before reclassifications, before tax	159	298	499	1,305
Other comprehensive income (loss) before reclassifications, tax	(27)	(68)	(96)	(284)
Other comprehensive income (loss) before reclassifications, after-tax	132	230	403	1,021
Reclassification adjustment, before tax	(16)	(10)	(3)	(17)
Reclassification adjustment, tax	4	3	1	4
Net amounts reclassified from AOCI to net income	(12)	(7)	(2)	(13)
Shareholders other comprehensive income (loss), net of tax	120	223	401	1,008
Ending balance	1,376	1,026	1,376	1,026
Translation of foreign currencies
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(374)	(285)	(275)	(221)
Other comprehensive income (loss), before reclassifications, before tax, including temporary equity	102	(124)	7	(191)
Other comprehensive income (loss) before reclassifications, tax, including temporary equity	7	(3)	(3)	(4)
Other comprehensive income, net of tax	109	(127)	4	(195)
Less: Net translation of foreign currencies attributable to noncontrolling interests	(4)	1	(10)	(3)
Shareholders other comprehensive income (loss), net of tax	113	(128)	14	(192)
Ending balance	(261)	(413)	(261)	(413)
Postretirement benefits liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,670)	(1,483)	(1,641)	(1,508)
Other comprehensive income (loss) before reclassifications, before tax	0	(1)	(73)	(9)
Other comprehensive income (loss) before reclassifications, tax	0	0	17	1
Other comprehensive income (loss) before reclassifications, after-tax	0	(1)	(56)	(8)
Reclassification adjustment, tax	(4)	(3)	(13)	(12)
Net amounts reclassified from AOCI to net income	14	13	41	45
Shareholders other comprehensive income (loss), net of tax	14	12	(15)	37
Ending balance	(1,656)	(1,471)	(1,656)	(1,471)
Reclassification adjustment for amortization of net losses from past experience and prior service costs (interest expense and other)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, before tax	18	16	54	47
Reclassification adjustment for settlement (interest expense and other)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, before tax	$ 0	$ 0	$ 0	$ 10