Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Partners' Capital [Abstract]
Net income	$ 77,615	$ 60,444	$ 205,273	$ 175,295
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss during the period	9,464	(551)	76,007	(95,920)
Change in net unrealized gain on securities transferred to held to maturity	(8,746)	(8,054)	(27,119)	(26,258)
Reclassification adjustment for net (gains) losses included in net income	(33)	14	(35)	3
Total securities available for sale and transferred securities	685	(8,591)	48,853	(122,175)
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	672	1,640	2,015	4,919
Derivatives:
Change in the accumulated gain/loss on effective cash flow hedge derivatives	0	(15)	0	(48)
Reclassification adjustments for (gains) losses included in net income:
Interest rate swaps on variable-rate loans	(9,345)	(9,345)	(28,035)	(28,035)
Interest rate swap on junior subordinated deferrable interest debentures	0	1,120	0	3,308
Total derivatives	(9,345)	(8,240)	(28,035)	(24,775)
Other comprehensive income (loss), before tax	(7,988)	(15,191)	22,833	(142,031)
Deferred tax expense (benefit) related to other comprehensive income	(2,796)	(5,316)	7,991	(49,710)
Other comprehensive income (loss), net of tax	(5,192)	(9,875)	14,842	(92,321)
Comprehensive income	$ 72,423	$ 50,569	$ 220,115	$ 82,974