Non-consolidated variable interest entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Sep. 30, 2011 Prlp2011 Holdings Llc Joint Venture [Member]	Jun. 30, 2012 Prlp2011 Holdings Llc Joint Venture [Member]	Jun. 30, 2012 Fnma Gnma Vie [Member]	Dec. 31, 2011 Fnma Gnma Vie [Member]
Variable Interest Entity [Line Items]
Principal Amount Outstanding on Loans Securitized or Asset-backed Financing Arrangement			$ 11,100	$ 9,400
Variable Interest Entity Activity Between VIE And Entity Other Measure Of Activity Description		The Corporation determined that the maximum exposure to loss under a worst case scenario at June 30, 2012 would be not recovering the carrying amount of the acquisition loan, the advances on the advance facility and working capital line, and the equity interest held by the Corporation, net of the deposits.	Maximum exposure to loss represents the maximum loss, under a worst case scenario, that would be incurred by the Corporation, as servicer for the VIEs, assuming all loans serviced are delinquent and that the value of the Corporation’s interests and any associated collateral declines to zero, without any consideration of recovery.
Equity Method Investment Ownership Percentage	24.90%	24.90%
Loans Receivable, Description of Variable Rate Basis	5-year maturity and bears a variable interest at 30-day LIBOR plus 300 basis points
Variable Interest Entity, Qualitative or Quantitative Information, Size of VIE	In September of 2011, BPPR sold construction and commercial real estate loans with a fair value of $##D million
Purchase Price Of Loans	57.00%
Financed Closing Costs	2
Carrying Amount Of Acquisition Loan Before Financed Closing Costs	84
Carrying Amount Of Acquisition Loan After Financed Closing Costs	86
Total Working Capital Line	20
Total Advance Facility	68.5
Cash Received From Investee	$ 48