Litigation and contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011
Class action complaint under RESPA [Abstract]
Mortgage lenders named as defendants in class action complaints	2
Discrimination complaint - U.S. Department of Housing and Urban Development [Abstract]
Number of employees named in an administrative action	2
Amount of aggregate fines related to the administrative action	$ 48,000
Class action complaints - Fulton County Employees' Retirement System [Abstract]
Number of previously filed purported class action complaints	5
Number of officers of C-BASS named as defendants in complaint	2
Number of officers named as defendants in amended complaint	2
Number of officers of C-BASS named as defendants in amended complaint	2
Countrywide dispute [Abstract]
Mitigation of paid losses	435,000,000
Average claims payment had the loans not been rescinded (per loan)	72,100
Amount of damages sought	700,000,000
Number of loans that each of the plaintiff and the defendant have selected	12
Number of members on arbitration panel	3
Total number of loans selected by both plaintiff and defendant combined	24
Expected delay in hearing start date (in days)	60D
Number of loans in primary delinquency inventory related to plaintiff	38,127
Percentage of loans in primary delinquency inventory related to plaintiff (in hundredths)	22.00%
Claims paid (in hundredths)	78.00%
Claims rescinded (in hundredths)	22.00%
Mitigation of incurred losses since January 2008	3,100,000,000
Mitigation on paid losses, excluding deductible amounts	2,600,000,000
Amount excluded from mitigation on paid losses that would have been applied to a deductible	600,000,000
Total loss reserves, estimated benefit from rescissions	700,000,000
Freddie Mac dispute [Abstract]
Difference in aggregate loss limit under pool insurance policy	535,000,000
Impact of aggregate loss limit difference under pool insurance policy on results of operations	$ 192,000,000
Pending or Threatened Litigation [Member] | U.S. District Court for the Central District of California [Member]
Class action complaint under RESPA [Abstract]
Mortgage insurers named as defendants in class action	7
Pending or Threatened Litigation [Member] | U.S. District Court for the Eastern District of Pennsylvania [Member]
Class action complaint under RESPA [Abstract]
Mortgage insurers named as defendants in class action	7