Mortgage Servicing Rights - Schedule of Changes in the Fair Value of Residential First Mortgage MSRs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Servicing Asset at Fair Value
Balance at beginning of period	$ 290
Fair value of MSRs at end of period	291	$ 290
Residential first mortgage
Servicing Asset at Fair Value
Balance at beginning of period	290	291	$ 335
Additions from loans sold with servicing retained	223	356	288
Reductions from sales	(57)	(339)	(310)
Decrease in MSR fair value due to pay-offs, pay-downs, run-off, model changes, and other			(31)
Changes in estimates of fair value due to interest rate risk			9
Fair value of MSRs at end of period	291	290	291
Net (loss) return on mortgage servicing rights \| Residential first mortgage
Servicing Asset at Fair Value
Decrease in MSR fair value due to pay-offs, pay-downs, run-off, model changes, and other	(89)	(20)	(31)
Changes in estimates of fair value due to interest rate risk	$ (76)	$ 2	$ 9

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Decrease in servicing assets subsequently measured at fair value resulting from conveyance of servicing rights to unrelated parties.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
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-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

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Amount of increase (decrease) from changes in fair value classified as other for a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

The increase (decrease) in the fair value of servicing assets that are subsequently measured at fair value.

+ References

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