Mortgage Servicing Assets - Schedule of Range and Weighted-Average of Significant Unobservable Inputs (Details) - Discounted Cash Flow [Member] - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Commercial Mortgage Backed Securities [Member] \| Minimum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	1.00%	1.00%
Residual cash flows discount rate (as a percent)	7.00%	7.00%
Escrow earn rate (as a percent)	2.56%	0.90%
Loan assumption rate (as a percent)	0.00%	0.00%
Commercial Mortgage Backed Securities [Member] \| Maximum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	2.00%	3.00%
Residual cash flows discount rate (as a percent)	15.00%	15.00%
Escrow earn rate (as a percent)	4.20%	3.10%
Loan assumption rate (as a percent)	3.22%	3.00%
Commercial Mortgage Backed Securities [Member] \| Weighted Average [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	1.14%	1.20%
Residual cash flows discount rate (as a percent)	9.18%	9.10%
Escrow earn rate (as a percent)	3.35%	2.50%
Loan assumption rate (as a percent)	1.35%	1.22%
Residential Mortgage Backed Securities [Member] \| Minimum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	7.50%	8.50%
Prepayment speed (as a percent)	8.45%	9.16%
Servicing cost	$ 62,000,000	$ 76,000,000
Residential Mortgage Backed Securities [Member] \| Maximum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	10.00%	11.00%
Prepayment speed (as a percent)	56.11%	51.52%
Servicing cost	$ 5,125,000,000	$ 4,385,000,000
Residential Mortgage Backed Securities [Member] \| Weighted Average [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	7.54%	8.54%
Prepayment speed (as a percent)	9.08%	10.46%
Servicing cost	$ 68,250,000	$ 83,110,000

Interest rate used to account for mortgage loan at fair value upon assumption.

No definition available.

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- Definition

Mortgage servicing assets interest rate for mortgage funds.

+ References

No definition available.

+ Details

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- Definition

Mortgage servicing assets servicing cost.

+ References

No definition available.

+ Details

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- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746

+ Details

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- Definition

Percentage of contractually collectible principal associated with a financial asset expected not to be collected due to default by the borrower.

+ References

+ Details

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- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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