Commercial Mortgage Residual Interests (Securitizations) (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2016 securitizations	Dec. 31, 2016 securitizations	Dec. 31, 2015 securitization
Commercial Mortgage Residual Interests [Abstract]
Number of securitizations	5	5	7
Remaining number of securitizations		2