TWO Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Average Notional Amounts of Derivative Positions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Inverse Interest-Only Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	$ 1,922,195
Derivative Liability, Average Notional Amount	0
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	0
Derivative Liability, Average Notional Amount	14,854,500	6,366,593
Credit Default Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	437,845
Derivative Liability, Average Notional Amount	0
Interest Rate Swaption [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	5,542,778
Derivative Liability, Average Notional Amount	0
Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	1,213,644
Derivative Liability, Average Notional Amount	326,667
Forward Purchase Commitment [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	51,783
Derivative Liability, Average Notional Amount	$ 0