Reclassifications of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ 180,161	$ 200,466	$ 557,636		$ 591,683
Tax expense (Benefit)	65,961	71,668	202,244		213,420
Net gain on sales of securities, net of tax	614	306	3,709		833
Total reclassifications for the period			(676)	[1]
Reclassification out of Accumulated Other Comprehensive Income (loss) | Unrealized gains on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gain on sales of securities			6,212	[1]
Tax expense (Benefit)			(2,503)	[1]
Net gain on sales of securities, net of tax			3,709	[1]
Reclassification out of Accumulated Other Comprehensive Income (loss) | Amortization of defined benefit pension
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs			187	[1],[2]
Actuarial losses			(7,547)	[1],[2]
Total before tax			(7,360)	[1]
Tax expense (Benefit)			2,975	[1]
Amortization of defined benefit pension items, net of tax			$ (4,385)	[1]

[1] Amounts in parentheses indicate expense items.

[2] These components of AOCL are included in the computation of net periodic (credit) expense. (Please see Note 9, Pension and Other Post-Retirement Benefits, for additional information).