Long-Term Debt (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended		12 Months Ended					0 Months Ended											0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	May 03, 2013	Jun. 21, 2012	Sep. 16, 2013 Series C Preferred Stock [Member]	Dec. 31, 2013 Parent Company [Member]	Dec. 31, 2013 4.00%	Dec. 31, 2013 4.50%	Dec. 31, 2013 Senior Medium-Term Note two point five five percent to five point five zero percent [Member]	Dec. 31, 2013 Senior medium-term notes, optional early redemptions as of December 31, 2012 [Member]	Dec. 31, 2013 Senior medium-term notes, optional early redemptions in 2013 [Member]	Dec. 31, 2013 Senior medium-term notes, optional early redemptions in 2014 [Member]	Dec. 31, 2013 Senior medium-term notes, optional early redemptions in 2015 [Member]	Dec. 31, 2013 Junior subordinated debentures payable to ZCTB and Stockmen's Trust II and III [Member]	Dec. 31, 2013 Medium-term Notes [Member]	Sep. 15, 2023 Subordinated Notes Interest Rate 6.95 Percent [Member]	Dec. 31, 2013 Subordinated Notes Interest Rate 6.95 Percent [Member]	Dec. 15, 2013 Subordinated Notes Interest Rate 6.95 Percent [Member]	Nov. 15, 2018 Subordinated Notes Interest Rate 5.65 Percent [Member]	May 15, 2014 Subordinated Notes Interest Rate 5.65 Percent [Member]	Dec. 31, 2013 Subordinated Notes Interest Rate 5.65 Percent [Member]
Debt Instrument [Line Items]
New interest rate																			3mL+3.89%			3mL+4.19%
Interest payments begin																					Dec. 15, 2013		May 15, 2014
Earliest possible redemption date																				Sep. 15, 2023				Nov. 15, 2018
Remaining subordinated notes after exchanged, par value	$ 1,200,000,000		$ 1,200,000,000
Stock Redeemed or Called During Period, Value			799,468,000	(1,542,500,000)				800,000,000
Subordinated debt converted to preferred stock			1,210,000	89,564,000	256,109,000
Reduction of interest expenses on debt, amortization amount	3,800,000	7,800,000
Senior medium-term notes	1,454,779,000	1,325,630,000	1,454,779,000	1,325,630,000						196,103,000	388,467,000	335,628,000
Senior medium-term notes with early redemption option	267,593,000		267,593,000										135,305,000	93,899,000	27,281,000	11,108,000
Subordinated debt repurchases from tender offer			250,000,000
Senior debt repurchases from tender offer			258,000,000
Trust Preferred Securities Rate, Redeemed						8.00%
Trust Preferred Securities, Shares Redeemed						11.4
Preferred Stock, Liquidation Preference, Value						1.00
Preferred Stock, Liquidation Preference Per Share	$ 1,000		$ 1,000			$ 25
Preferred Stock, Redemption Amount						285,000,000
Debt extinguishment cost			120,192,000	0	0
Redemption Premium			(45,800,000)
Write off of unamortized debt discount and issuance costs			(74,400,000)
Variable rate senior medium-term notes guaranteed under the FDIC's Temporary Liquidity Guarantee Program							254,900,000
Federal home loan bank loan maturity range from	Jun. 01, 2014
Federal home loan bank loan maturity range to	Sep. 01, 2041
FHLB advances interest rate, minimum	2.808%		2.808%
FHLB advances interest rate, maximum	6.983%		6.983%
FHLB advances weighted average interest rate on advances outstanding	4.50%	4.50%	4.50%	4.50%
Long-term debt, Parent only maturities	$ 767,073,000		$ 767,073,000						$ 591,400,000								$ 15,500,000	$ 575,900,000