Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 26,957	$ 25,318
Ending balance	28,876	26,196
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(616)	(1,066)
Beginning balance	157	276
Beginning balance	(459)	(790)
Other comprehensive income (loss) before reclassifications:	284	(368)
Other comprehensive income (loss) before reclassifications, tax	(72)	92
OCI, before reclassifications, net of tax, attributable to parent	212	(276)
Total other comprehensive income (loss)	580	(200)
Deferred income taxes and credits	(148)	48
Other comprehensive income (loss), net of Tax, Portion attributable to parent	432	(152)
Equity, attributable to parent, ending balance	(36)	(1,266)
Ending balance	9	324
Ending balance	(27)	(942)
Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(251)	(444)
Beginning balance	(187)
Other comprehensive income (loss) before reclassifications:	307	(2)
Other comprehensive income (loss) before reclassifications, tax	(78)	1
OCI, before reclassifications, net of tax, attributable to parent	229	(1)
Amounts reclassified from accumulated other comprehensive income (loss) that (increase) decrease net income:	13
Reclassification from AOCI, current period, tax	(4)
Reclassification from AOCI, current period, net of tax, attributable to parent	9
Total other comprehensive income (loss)	320	(2)
Equity, attributable to parent, ending balance	69	(446)
Ending balance	51
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(203)	(336)
Beginning balance	(151)
Other comprehensive income (loss) before reclassifications:	(26)	(366)
Other comprehensive income (loss) before reclassifications, tax	7	91
OCI, before reclassifications, net of tax, attributable to parent	(19)	(275)
Amounts reclassified from accumulated other comprehensive income (loss) that (increase) decrease net income:	288	173
Reclassification from AOCI, current period, tax	(73)	(44)
Reclassification from AOCI, current period, net of tax, attributable to parent	215	129
Total other comprehensive income (loss)	262	(193)
Equity, attributable to parent, ending balance	59	(529)
Ending balance	45
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(155)	(273)
Beginning balance	(115)
Other comprehensive income (loss) before reclassifications:	0	0
Total other comprehensive income (loss)	(5)	(5)
Equity, attributable to parent, ending balance	(160)	(278)
Ending balance	(119)
Prior Service Credit
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss) that (increase) decrease net income:	(2)	(1)
Reclassification from AOCI, current period, tax	0	0
Reclassification from AOCI, current period, net of tax, attributable to parent	(2)	(1)
Actuarial Gains
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss) that (increase) decrease net income:	(3)	(4)
Reclassification from AOCI, current period, tax	1	0
Reclassification from AOCI, current period, net of tax, attributable to parent	(2)	(4)
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(7)	(13)
Beginning balance	(6)
Other comprehensive income (loss) before reclassifications:	3	0
Other comprehensive income (loss) before reclassifications, tax	(1)
OCI, before reclassifications, net of tax, attributable to parent	2
Total other comprehensive income (loss)	3	0
Equity, attributable to parent, ending balance	(4)	$ (13)
Ending balance	$ (4)