Fair Value Measurements Fair Value Measurements Narrative Tagging (Details)	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Tolerable Range of Difference in Valuation	7.50%
Effective rate - minimum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	4.20%	4.60%
Effective rate - minimum [Member] | Public housing capital fund trusts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	3.50%	3.90%
Effective rate - minimum [Member] | Bond Purchase Commitment [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	4.80%	5.40%
Effective rate - minimum [Member] | Taxable Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	3.60%	4.20%
Effective rate - maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	11.50%	12.10%
Effective rate - maximum [Member] | Public housing capital fund trusts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	5.20%	5.70%
Effective rate - maximum [Member] | Bond Purchase Commitment [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	10.30%	10.90%
Effective rate - maximum [Member] | Taxable Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	8.30%	10.50%