Mortgage Loans Credit Quality Indicators - MF (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 3,040,217	$ 3,035,712
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	207,956	200,174
Multifamily [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	202,213	194,132
Multifamily [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	3,145	3,202
Multifamily [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,597	2,833
Multifamily [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 1	$ 7