Securities - Significant Assumptions (Details) - Non-agency residential	Sep. 30, 2017
Weighted Average
Significant Assumptions:
Prepayment speed	12.00%
Loss severity	19.80%
Life default rate	21.00%
Weighted Average \| Prime
Significant Assumptions:
Loss severity	17.50%
Life default rate	15.60%
Weighted Average \| Alt-A
Significant Assumptions:
Loss severity	18.40%
Life default rate	21.70%
Weighted Average \| Subprime
Significant Assumptions:
Loss severity	29.50%
Life default rate	22.10%
10th Percentile
Significant Assumptions:
Prepayment speed	3.00%
Loss severity	9.10%
Life default rate	1.20%
90th Percentile
Significant Assumptions:
Prepayment speed	20.60%
Loss severity	36.50%
Life default rate	77.70%