Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 29,027	$ 26,957
Ending balance	28,991	27,169
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(219)	(616)
Beginning balance	55	157
Beginning balance	(164)	(459)
Other comprehensive income (loss) before reclassifications:	289	(258)
Other comprehensive income (loss) before reclassifications, tax	(73)	62
OCI, before reclassifications, net of tax, attributable to parent	216	(196)
Total other comprehensive income (loss)	340	(171)
Deferred income taxes and credits	(86)	41
Other comprehensive income (loss), net of Tax, Portion attributable to parent	254	(130)
Equity, attributable to parent, ending balance	121	(787)
Ending balance	(31)	198
Ending balance	90	(589)
Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(205)	(251)
Beginning balance	(153)
Other comprehensive income (loss) before reclassifications:	197	(13)
Other comprehensive income (loss) before reclassifications, tax	(50)	2
OCI, before reclassifications, net of tax, attributable to parent	147	(11)
Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:		1
Reclassification from AOCI, current period, net of tax, attributable to parent		1
Total other comprehensive income (loss)	197	(12)
Equity, attributable to parent, ending balance	(8)	(263)
Ending balance	(6)
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(135)	(203)
Beginning balance	(101)
Other comprehensive income (loss) before reclassifications:	91	(243)
Other comprehensive income (loss) before reclassifications, tax	(23)	60
OCI, before reclassifications, net of tax, attributable to parent	68	(183)
Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:	53	87
Reclassification from AOCI, current period, tax	(13)	(21)
Reclassification from AOCI, current period, net of tax, attributable to parent	40	66
Total other comprehensive income (loss)	144	(156)
Equity, attributable to parent, ending balance	9	(359)
Ending balance	7
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	131	(155)
Beginning balance	98
Other comprehensive income (loss) before reclassifications:	0	0
Total other comprehensive income (loss)	(2)	(1)
Equity, attributable to parent, ending balance	129	(156)
Ending balance	96
Actuarial Gains
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive income 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)
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, attributable to parent, beginning balance	(10)	(7)
Beginning balance	(8)
Other comprehensive income (loss) before reclassifications:	1	(2)
Other comprehensive income (loss) before reclassifications, tax	0	0
OCI, before reclassifications, net of tax, attributable to parent	1	(2)
Total other comprehensive income (loss)	1	(2)
Equity, attributable to parent, ending balance	(9)	$ (9)
Ending balance	$ (7)