Fair Value - Level 3 Unobservable Inputs, Mortgage Loans and IRLC (Details) - item	Sep. 30, 2018	Dec. 31, 2017
Mortgage loans held for sale | Discount rate | Level 3 | Minimum
Excess servicing spread financing
Input	2.8	2.9
Mortgage loans held for sale | Discount rate | Level 3 | Maximum
Excess servicing spread financing
Input	9.2	10.0
Mortgage loans held for sale | Discount rate | Level 3 | Weighted average
Excess servicing spread financing
Input	2.9	2.9
Mortgage loans held for sale | Twelve-month projected housing price index Change | Level 3 | Minimum
Excess servicing spread financing
Input	3.5	3.1
Mortgage loans held for sale | Twelve-month projected housing price index Change | Level 3 | Maximum
Excess servicing spread financing
Input	6.1	5.6
Mortgage loans held for sale | Twelve-month projected housing price index Change | Level 3 | Weighted average
Excess servicing spread financing
Input	3.9	3.6
Mortgage loans held for sale | Prepayment/resale speed | Level 3 | Minimum
Excess servicing spread financing
Input	0.1	0.2
Mortgage loans held for sale | Prepayment/resale speed | Level 3 | Maximum
Excess servicing spread financing
Input	71.0	72.2
Mortgage loans held for sale | Prepayment/resale speed | Level 3 | Weighted average
Excess servicing spread financing
Input	24.2	44.6
Mortgage loans held for sale | Total prepayment speed | Level 3 | Minimum
Excess servicing spread financing
Input	0.1	0.2
Mortgage loans held for sale | Total prepayment speed | Level 3 | Maximum
Excess servicing spread financing
Input	72.1	75.2
Mortgage loans held for sale | Total prepayment speed | Level 3 | Weighted average
Excess servicing spread financing
Input	41.3	55.8
Interest rate lock commitments | Pull-through rate | Level 3 | Minimum
Excess servicing spread financing
Input	16.6	25.0
Interest rate lock commitments | Pull-through rate | Level 3 | Maximum
Excess servicing spread financing
Input	100.0	100.0
Interest rate lock commitments | Pull-through rate | Level 3 | Weighted average
Excess servicing spread financing
Input	85.7	85.6
Interest rate lock commitments | Mortgage servicing rights value expressed as servicing fee multiple | Level 3 | Minimum
Excess servicing spread financing
Input	1.6	1.4
Interest rate lock commitments | Mortgage servicing rights value expressed as servicing fee multiple | Level 3 | Maximum
Excess servicing spread financing
Input	5.9	5.8
Interest rate lock commitments | Mortgage servicing rights value expressed as servicing fee multiple | Level 3 | Weighted average
Excess servicing spread financing
Input	4.0	4.0
Interest rate lock commitments | Percentage of unpaid principal balance | Level 3 | Minimum
Excess servicing spread financing
Input	0.4	0.3
Interest rate lock commitments | Percentage of unpaid principal balance | Level 3 | Maximum
Excess servicing spread financing
Input	2.8	3.0
Interest rate lock commitments | Percentage of unpaid principal balance | Level 3 | Weighted average
Excess servicing spread financing
Input	1.4	1.4
Repurchase agreement derivatives
Excess servicing spread financing
Acceptance rate (as a percent)	97.00%	97.00%