Securities - Significant Assumptions (Details) - Non-agency residential	Jun. 30, 2018
Weighted Average
Significant Assumptions:
Prepayment speed	13.00%
Loss severity	19.90%
Life default rate	17.90%
Weighted Average \| Prime
Significant Assumptions:
Loss severity	16.80%
Life default rate	15.60%
Weighted Average \| Alt-A
Significant Assumptions:
Loss severity	17.10%
Life default rate	17.30%
Weighted Average \| Subprime
Significant Assumptions:
Loss severity	26.90%
Life default rate	20.00%
10th Percentile
Significant Assumptions:
Prepayment speed	3.20%
Loss severity	9.00%
Life default rate	1.50%
90th Percentile
Significant Assumptions:
Prepayment speed	21.40%
Loss severity	36.90%
Life default rate	67.10%