Parent company financial statements - Condensed Statement of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities
Net income	$ 1,029,498	$ 859,479	$ 736,161
Adjustments to reconcile net income to net cash provided by operating activities
Provision for deferred income taxes	131,858	33,924	51,068
Asset write-downs	63,790	170,632	101,106
Net cash provided by operating activities	499,981	1,772,246	1,675,647
Cash flows from investing activities
Other, net	(120,610)	21,126	(927)
Net cash provided (used) by investing activities	(4,060,858)	368,932	475,410
Cash flows from financing activities
Payments on long-term borrowings	(2,080,167)	(1,809,984)	(2,514,342)
Dividends paid - common	(357,717)	(350,129)	(335,303)
Dividends paid - preferred	(53,450)	(48,203)	(40,225)
Proceeds from issuance of preferred stock		495,000
Redemption of preferred stock		(370,000)
Other, net	63,616	31,177	69,381
Net cash provided (used) by financing activities	4,095,095	(1,622,536)	(2,463,644)
Net increase (decrease) in cash and cash equivalents	534,218	518,642	(312,587)
Cash and cash equivalents at beginning of year	1,452,397	933,755	1,246,342
Cash and cash equivalents at end of year	1,986,615	1,452,397	933,755
Supplemental disclosure of cash flow information
Interest received during the year	2,931,409	2,807,071	2,765,101
Interest paid during the year	371,887	440,810	490,767
Income taxes received during the year	405,598	251,810	287,740
Parent Company [Member]
Cash flows from operating activities
Net income	1,029,498	859,479	736,161
Adjustments to reconcile net income to net cash provided by operating activities
Equity in undistributed income of subsidiaries	(400,617)	(228,748)	(317,468)
Provision for deferred income taxes	1,724	(10,349)	2,237
Asset write-downs		79,012
Net change in accrued income and expense	6,798	44,336	43,567
Net cash provided by operating activities	637,403	743,730	464,497
Cash flows from investing activities
Proceeds from sales of investment securities	411	1,987	2,591
Proceeds from maturities of investment securities		4,400	1,150
Purchases of investment securities			(2,225)
Purchase of Wilmington Trust Corporation preferred stock		(330,000)
Other, net	324	2,833	1,033
Net cash provided (used) by investing activities	735	(320,780)	2,549
Cash flows from financing activities
Payments on long-term borrowings	(300,000)
Dividends paid - common	(357,717)	(350,129)	(335,303)
Dividends paid - preferred	(53,450)	(48,203)	(40,225)
Proceeds from issuance of preferred stock		495,000
Redemption of preferred stock		(370,000)
Other, net	143,352	16,386	63,122
Net cash provided (used) by financing activities	(567,815)	(256,946)	(312,406)
Net increase (decrease) in cash and cash equivalents	70,323	166,004	154,640
Cash and cash equivalents at beginning of year	649,128	483,124	328,484
Cash and cash equivalents at end of year	719,451	649,128	483,124
Supplemental disclosure of cash flow information
Interest received during the year	1,970	2,082	1,581
Interest paid during the year	80,090	87,184	87,456
Income taxes received during the year	$ 21,878	$ 57,964	$ 50,882