Parent Company Financial Statements - Condensed Statement of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net Income (Loss)	$ 2,741	$ 1,992	$ 1,859
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for deferred income taxes	(97)	(30)	87
Net cash provided by operating activities	3,905	4,574	2,715
Cash flows from investing activities
Other, net	(440)	(620)	(511)
Cash flows from financing activities
Proceeds from long-term borrowings	5,035	999	10
Payments on long-term borrowings	(824)	(907)	(853)
Purchases of treasury stock	(594)	(1,800)
Dividends paid — common	(868)	(784)	(580)
Dividends paid — preferred	(100)	(97)	(68)
Proceeds from issuance of Series I preferred stock			495
Other, net	18	(14)	(28)
Net increase (decrease) in cash, cash equivalents and restricted cash	211	182	(215)
Supplemental disclosure of cash flow information
Interest received during the year	10,092	6,135	3,977
Income taxes received during the year	452	488	314
Parent Company [Member]
Cash flows from operating activities
Net Income (Loss)	2,741	1,992	1,859
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed income of subsidiaries	(847)	448	(855)
Provision for deferred income taxes	(5)	7	10
Net change in accrued income and expense	32	8	(23)
Net cash provided by operating activities	1,921	2,455	991
Cash flows from investing activities
Net investment in consolidated subsidiaries	(1)	54	(199)
Acquisition, net of cash consideration		538
Other, net	(41)	24	(3)
Net cash provided (used) by investing activities	(42)	616	(202)
Cash flows from financing activities
Repayment of short-term borrowings assumed in acquisition		(500)
Proceeds from long-term borrowings	1,998	499
Payments on long-term borrowings	(750)
Purchases of treasury stock	(594)	(1,800)
Dividends paid — common	(868)	(784)	(580)
Dividends paid — preferred	(100)	(97)	(68)
Other, net	14	2	(7)
Net cash used by financing activities	(300)	(2,680)	(160)
Net increase (decrease) in cash, cash equivalents and restricted cash	1,579	391	629
Cash and cash equivalents at beginning of year	1,820	1,429	800
Cash and cash equivalents at end of year	3,399	1,820	1,429
Supplemental disclosure of cash flow information
Interest received during the year	6	1	1
Interest paid during the year	135	49	20
Income taxes received during the year	$ 43	$ 28	53
Parent Company [Member] | Series I Preferred Stock [Member]
Cash flows from financing activities
Proceeds from issuance of Series I preferred stock			$ 495