Non-consolidated variable interest entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Sep. 30, 2011	Sep. 30, 2012	Dec. 31, 2011
Prlp2011 Holdings Llc Joint Venture [Member]
Variable Interest Entity [Line Items]
Equity Method Investment Ownership Percentage	24.90%	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 $148 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
Fnma Gnma Fhlmc Vie [Member]
Variable Interest Entity [Line Items]
Principal Amount Outstanding on Loans Securitized or Asset-backed Financing Arrangement		10,800	9,400