Fair Value Measurements Fair Value Measurements Narrative Tagging (Details)	Dec. 31, 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	4.90%	4.20%
Effective rate - minimum [Member] | Public housing capital fund trusts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	4.30%	3.90%
Effective rate - maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	12.40%	12.10%
Effective rate - maximum [Member] | Public housing capital fund trusts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effective rate	6.00%	5.70%