Securities - Significant Assumptions (Details) - Non-agency residential	Sep. 30, 2018
Weighted Average
Significant Assumptions:
Prepayment speed	12.00%
Loss severity	18.10%
Life default rate	20.10%
Weighted Average \| Prime
Significant Assumptions:
Loss severity	16.20%
Life default rate	16.10%
Weighted Average \| Alt-A
Significant Assumptions:
Loss severity	16.40%
Life default rate	21.90%
Weighted Average \| Subprime
Significant Assumptions:
Loss severity	22.20%
Life default rate	22.70%
10th Percentile
Significant Assumptions:
Prepayment speed	3.10%
Loss severity	8.40%
Life default rate	0.70%
90th Percentile
Significant Assumptions:
Prepayment speed	23.30%
Loss severity	31.00%
Life default rate	73.50%