Fair Value Accounting - Significant Unobservable Inputs (Details) (Mortgage-backed Securities, Issued by Private Enterprises [Member], Present Value Analysis [Member], Fair Value, Inputs, Level 3 [Member])	3 Months Ended
	Mar. 31, 2015
Fair Value Inputs, Quantitative Information [Line Items]
Fair value inputs, weighted average life, in years	2 years
Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Fair value inputs, prepayment rates	5.50%
Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Fair value inputs, prepayment rates	9.40%