Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 45,338
Other comprehensive (loss) income, net of tax	(590)	$ 427
Other comprehensive (loss) attributable to redeemable noncontrolling interest	(4)	(2)
Other comprehensive income, net of tax	(586)	429
Ending balance	45,079
Securities and Derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	975	18
Other comprehensive income (loss) before reclassifications, before tax	(580)	565
Other comprehensive income (loss) before reclassifications, tax	127	(122)
Other comprehensive income (loss) before reclassifications, after-tax	(453)	443
Reclassification adjustment, before tax	32	(1)
Reclassification adjustment, tax	(7)	0
Net amounts reclassified from AOCI to net income	25	(1)
Other comprehensive income, net of tax	(428)	442
Ending balance	547	460
Translation of foreign currencies
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(275)	(221)
Other comprehensive income (loss), before reclassifications, before tax, including temporary equity	(160)	(25)
Other comprehensive income (loss) before reclassifications, tax, including temporary equity	15	1
Other comprehensive (loss) income, net of tax	(175)	(26)
Other comprehensive (loss) attributable to redeemable noncontrolling interest	(4)	(2)
Other comprehensive income, net of tax	(171)	(24)
Ending balance	(446)	(245)
Postretirement benefits liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,641)	(1,508)
Reclassification adjustment, tax	(5)	(14)
Net amounts reclassified from AOCI to net income	13	11
Other comprehensive income, net of tax	13	11
Ending balance	(1,628)	(1,497)
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	15
Reclassification adjustment for settlement (interest expense and other)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, before tax	$ 0	$ 10