Mortgage Loans Credit Quality Indicators - MF (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 3,039,240	$ 3,047,794
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	198,699	189,233
Multifamily [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	192,767	182,079
Multifamily [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,725	3,070
Multifamily [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	3,203	3,842
Multifamily [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 4	$ 242