Parent Company Financial Statements - Condensed Statement of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities
Net income	$ 2,588	$ 2,741	$ 1,992
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for deferred income taxes	(27)	(97)	(30)
Net change in other accrued income and expense	282	561	(70)
Net cash provided by operating activities	3,610	3,905	4,574
Cash flows from investing activities
Acquisition, net of cash consideration	0	0	394
Other, net	(538)	(440)	(620)
Cash flows from financing activities
Proceeds from long-term borrowings	5,497	5,035	999
Payments on long-term borrowings	(1,009)	(824)	(907)
Proceeds from issuance of Series J preferred stock	733	0	0
Redemption of Series E preferred stock	(350)	0	0
Purchases of treasury stock	(396)	(594)	(1,800)
Dividends paid — common	(895)	(868)	(784)
Dividends paid — preferred	(138)	(100)	(97)
Other, net	114	18	(14)
Net increase in cash and cash equivalents	178	211	182
Supplemental disclosure of cash flow information
Interest received during the year	11,077	10,092	6,135
Income taxes received during the year	236	452	488
Parent Company
Cash flows from operating activities
Net income	2,588	2,741	1,992
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed income of subsidiaries	(1,438)	(847)	448
Provision for deferred income taxes	(8)	(5)	7
Net change in other accrued income and expense	(5)	32	8
Net cash provided by operating activities	1,137	1,921	2,455
Cash flows from investing activities
Net investment in consolidated subsidiaries	(30)	(1)	54
Advances to consolidated subsidiaries	(2,000)	0	0
Acquisition, net of cash consideration	0	0	538
Other, net	(64)	(41)	24
Net cash provided (used) by investing activities	(2,094)	(42)	616
Cash flows from financing activities
Repayment of short-term borrowings assumed in acquisition	0	0	(500)
Proceeds from long-term borrowings	2,341	1,998	499
Payments on long-term borrowings	(205)	(750)	0
Purchases of treasury stock	(396)	(594)	(1,800)
Dividends paid — common	(895)	(868)	(784)
Dividends paid — preferred	(138)	(100)	(97)
Other, net	111	14	2
Net cash provided (used) by financing activities	1,201	(300)	(2,680)
Net increase in cash and cash equivalents	244	1,579	391
Cash and cash equivalents at beginning of year	3,399	1,820	1,429
Cash and cash equivalents at end of year	3,643	3,399	1,820
Supplemental disclosure of cash flow information
Interest received during the year	76	6	1
Interest paid during the year	257	135	49
Income taxes received during the year	51	43	28
Parent Company | Series J Preferred Stock
Cash flows from financing activities
Proceeds from issuance of Series J preferred stock	733	0	0
Parent Company | Series E Preferred Stock
Cash flows from financing activities
Redemption of Series E preferred stock	$ (350)	$ 0	$ 0