Investment Securities (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, written down to fair value	$ 0	$ 0
Writedown to fair value	0	0
Available-for-sale, allowance for credit loss	0	0
Accrued interest for AFS securities	616,000,000	634,000,000
Write-offs of accrued interest receivable on AFS securities	0	0
Write-offs of accrued interest receivable on HTM securities		$ 0
Deposits [Member]
Debt Securities, Available-for-sale [Line Items]
Fair value of pledged securities	1,600,000,000
Federal Reserve Bank Advances [Member]
Debt Securities, Available-for-sale [Line Items]
Fair value of pledged securities	10,100,000,000
Federal Home Loan Bank of San Francisco [Member]
Debt Securities, Available-for-sale [Line Items]
Fair value of pledged securities	$ 43,800,000,000

Debt Securities, Available-for-Sale, Accrued Interest Writeoff

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- Definition

Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss

+ References

No definition available.

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- Definition

Debt Securities, Available-for-Sale, Writedown To Fair Value

+ References

No definition available.

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- Definition

Debt Securities, Held-to-Maturity, Accrued Interest Writeoff

+ References

No definition available.

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- Definition

Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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-Name Accounting Standards Codification
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-SubTopic 30
-Section 45
-Paragraph 1
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- Definition

Amount of writeoff of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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.

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- Definition

The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
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