Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012		Mar. 31, 2012	Dec. 31, 2011
Assets [Abstract]
Trading securities	$ 150,887			$ 214,102		$ 204,242
Available for sale securities	10,372,903			11,287,221		11,506,434
Fair value option securities	167,860			284,296		331,887
Mortgage servicing rights	140,863		132,889	100,812		89,653		91,783	86,783
Derviative contracts, net of cash margin, assets	377,325			338,106		435,653
Liabilities [Abstract]
Derivative contracts net of cash margin, liabilities	232,544			283,589		254,422
U.S. Government agency debentures [Member]
Assets [Abstract]
Trading securities	74,632			16,545		3,100
U.S. agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	26,129			86,361		119,835
Available for sale securities	7,981,387			9,889,821		10,654,821
Fair value option securities	163,567			257,040		305,445
Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	37,057			90,326		58,150
Available for sale securities	95,440			87,142		87,969
Other trading securities [Member]
Assets [Abstract]
Trading securities	13,069			20,870		23,157
U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	1,052			1,002		1,002
Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	230,900			325,163		331,722
Commercial mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	1,946,295			895,075		339,095
Other debt securities [Member]
Assets [Abstract]
Available for sale securities	35,362			36,389		36,456
Fair value option securities	4,293			770		0
Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	23,680			25,072		25,288
Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	58,787			27,557		30,081
Corporate debt securities [Member]
Assets [Abstract]
Fair value option securities	0			26,486		26,442
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Trading securities	150,887			214,102		204,242
Available for sale securities	10,372,903			11,287,221		11,506,434
Fair value option securities	167,860			284,296		331,887
Residential mortgage loans held for sale	230,511			293,762		325,102
Mortgage servicing rights	140,863	[1]		100,812	[1]	89,653	[1]
Derviative contracts, net of cash margin, assets	377,325	[2]		338,106	[2]	472,783	[2]
Other assets, private equity funds	27,799			28,169		28,792
Liabilities [Abstract]
Derivative contracts net of cash margin, liabilities	232,544	[2]		283,589	[2]	435,497	[2]
Fair Value, Measurements, Recurring [Member] | U.S. Government agency debentures [Member]
Assets [Abstract]
Trading securities	74,632			16,545		3,100
Fair Value, Measurements, Recurring [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	26,129			86,361		119,835
Available for sale securities	7,981,387			9,889,821		10,654,821
Fair value option securities	163,567			257,040		305,445
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	37,057			90,326		58,150
Available for sale securities	95,440			87,142		87,969
Fair Value, Measurements, Recurring [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	13,069			20,870		23,157
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	1,052			1,002		1,002
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	230,900			325,163		331,722
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	1,946,295			895,075		339,095
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	35,362			36,389		36,456
Fair value option securities	4,293			770
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	23,680			25,072		25,288
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	58,787			27,557		30,081
Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets [Abstract]
Fair value option securities				26,486		26,442
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Trading securities	0			0		0
Available for sale securities	1,052			5,167		7,914
Fair value option securities	0			0		0
Residential mortgage loans held for sale	0			0		0
Mortgage servicing rights	0	[1]		0	[1]	0	[1]
Derviative contracts, net of cash margin, assets	644	[2]		11,597	[2]	8,301	[2]
Other assets, private equity funds	0			0		0
Liabilities [Abstract]
Derivative contracts net of cash margin, liabilities	0	[2]		0	[2]	0	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Government agency debentures [Member]
Assets [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	0			0		0
Available for sale securities	0			0		0
Fair value option securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	0			0		0
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	1,052			1,002		1,002
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair value option securities	0			0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	0			4,165		6,912
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate debt securities [Member]
Assets [Abstract]
Fair value option securities				0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Trading securities	150,887			214,102		204,242
Available for sale securities	10,323,261			11,233,792		11,451,841
Fair value option securities	167,860			284,296		331,887
Residential mortgage loans held for sale	230,511			293,762		325,102
Mortgage servicing rights	0	[1]		0	[1]	0	[1]
Derviative contracts, net of cash margin, assets	376,681	[2]		326,509	[2]	464,482	[2]
Other assets, private equity funds	0			0		0
Liabilities [Abstract]
Derivative contracts net of cash margin, liabilities	232,544	[2]		283,589	[2]	435,497	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Government agency debentures [Member]
Assets [Abstract]
Trading securities	74,632			16,545		3,100
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	26,129			86,361		119,835
Available for sale securities	7,981,387			9,889,821		10,654,821
Fair value option securities	163,567			257,040		305,445
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	37,057			90,326		58,150
Available for sale securities	55,769			46,440		46,690
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	13,069			20,870		23,157
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	230,900			325,163		331,722
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	1,946,295			895,075		339,095
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	30,650			30,990		31,056
Fair value option securities	4,293			770
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	23,680			25,072		25,288
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	54,580			21,231		23,169
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate debt securities [Member]
Assets [Abstract]
Fair value option securities				26,486		26,442
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Trading securities	0			0		0
Available for sale securities	48,590			48,262		46,679
Fair value option securities	0			0		0
Residential mortgage loans held for sale	0			0		0
Mortgage servicing rights	140,863	[1]		100,812	[1]	89,653	[1]
Derviative contracts, net of cash margin, assets	0	[2]		0	[2]	0	[2]
Other assets, private equity funds	27,799			28,169		28,792
Liabilities [Abstract]
Derivative contracts net of cash margin, liabilities	0	[2]		0	[2]	0	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Government agency debentures [Member]
Assets [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	0			0		0
Available for sale securities	0			0		0
Fair value option securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	0			0		0
Available for sale securities	39,671			40,702		41,279
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	4,712			5,399		5,400
Fair value option securities	0			0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	4,207			2,161		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate debt securities [Member]
Assets [Abstract]
Fair value option securities				$ 0		$ 0

[1] A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 5, Mortgage Banking Activities.

[2] See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded energy and agricultural derivative contacts, net of cash margin.