SECURITIES SOLD UNDER REPURCHASE AGREEMENTS AND OTHER BORROWINGS (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2012
Amount of securities sold under repurchase agreements
Total	$ 995,000,000	$ 1,020,208,000
Other disclosures
Total interest expense recorded on repurchase agreements	46,166,000	48,561,000	48,993,000
Other borrowings	20,000,000
Securities Sold Under Repurchase Agreements
Securities sold under repurchase agreements and other borrowings
Short-term repurchase agreements		25,200,000
Interest rates on short-term repurchase agreements (as a percent)		0.57%
Amount of long-term repurchase agreements modified	150,000,000			200,000,000
Reduction in interest rates on long-term repurchase agreements modified	1.95%			0.86%
Amount of securities sold under repurchase agreements
Total	995,000,000	1,020,208,000
Interest rate on securities sold under repurchase agreements
Total (as a percent)	4.30%	4.66%
Other disclosures
Total interest expense recorded on repurchase agreements	46,200,000	48,600,000	49,000,000
Available borrowing capacity from repurchase agreements	1,190,000,000	979,800,000
Securities Sold Under Repurchase Agreements | Minimum
Securities sold under repurchase agreements and other borrowings
Interest rates on long-term repurchase agreements (as a percent)	2.54%
Securities Sold Under Repurchase Agreements | Maximum
Securities sold under repurchase agreements and other borrowings
Interest rates on long-term repurchase agreements (as a percent)	5.01%
Securities Sold Under Repurchase Agreements | Maturities in Next Twelve Months
Amount of securities sold under repurchase agreements
Total		25,208,000
Interest rate on securities sold under repurchase agreements
Total (as a percent)		0.57%
Securities Sold Under Repurchase Agreements | Maturities in Year Four
Amount of securities sold under repurchase agreements
Total	245,000,000	245,000,000
Interest rate on securities sold under repurchase agreements
Total (as a percent)	4.49%	4.49%
Securities Sold Under Repurchase Agreements | Maturities in Year Five
Amount of securities sold under repurchase agreements
Total	350,000,000	700,000,000
Interest rate on securities sold under repurchase agreements
Total (as a percent)	4.96%	4.91%
Securities Sold Under Repurchase Agreements | Maturities in Year Six
Amount of securities sold under repurchase agreements
Total	50,000,000	50,000,000
Interest rate on securities sold under repurchase agreements
Total (as a percent)	4.15%	4.15%
Securities Sold Under Repurchase Agreements | Maturities in year ten
Amount of securities sold under repurchase agreements
Total	350,000,000
Interest rate on securities sold under repurchase agreements
Total (as a percent)	3.53%
Short term borrowings
Other disclosures
Other borrowings	$ 20,000,000
Maturity period of debt	2 days
Annual interest rate (as a percent)	0.25%