Fair Value Measurements (Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Residential Mortgage Loans Measured at Fair Value) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Residential mortgage loans
Aggregate fair value
Loans measured at fair value	$ 1,447	$ 716
Past due loans of 90 days or more	2	2
Non accrual loans	1	2
Aggregate unpaid principal balance
Loans measured at fair value	1,410	696
Past due loans of 90 days or more	2	2
Non accrual loans	1	2
Difference
Loans measured at fair value	37	20
Past due loans of 90 days or more	0	0
Non accrual loans	$ 0	0
Commercial loans
Aggregate fair value
Loans measured at fair value		7
Aggregate unpaid principal balance
Loans measured at fair value		7
Difference
Loans measured at fair value		$ 0

Fair value option loans held as assets 90 days or more past due aggregate unpaid principal.

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- Definition

Fair value option loans held as assets aggregate unpaid principal balance abstract.

+ References

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- Definition

Fair value option loans held as assets amount in non accrual status aggregate unpaid principal.

+ References

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- Definition

Fair value portion loans receivable disclosure.

+ References

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- Definition

Mortgages held for sale unpaid principal.

+ References

No definition available.

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- Definition

This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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- Definition

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are 90 days or more past due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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- Definition

This item represents the aggregate fair value of loans held as assets that are in nonaccrual status for which the fair value option has been elected, if the entity's policy is to recognize interest income separately from other changes in fair value.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(2)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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-Paragraph 28
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-Paragraph 28
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