Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other equity investments	$ 158,000,000	$ 134,000,000
Impairment loss (less than)	1,000,000
Loans, net of allowance	101,351,000,000	93,746,000,000
Discontinued operations \| Education Lending
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans at fair value	2,000,000	2,000,000
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	620,000,000	605,000,000
Loans at fair value	8,000,000	4,000,000
Carrying Amount \| Discontinued operations \| Education Lending
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	701,000,000	855,000,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	620,000,000	605,000,000
Loans at fair value	8,000,000	4,000,000
Fair Value \| Discontinued operations \| Education Lending
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	593,000,000	729,000,000
Level 3 \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	552,000,000	528,000,000
Loans at fair value	8,000,000	4,000,000
Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	81,000,000	90,000,000
Liabilities measured at fair value on non recurring basis	986,000,000	903,000,000
Recurring \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	13,000,000	13,000,000
Liabilities measured at fair value on non recurring basis	15,000,000	9,000,000
Nonrecurring \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities measured at fair value on non recurring basis	0	0
Principal investments, Direct \| Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	1,000,000	1,000,000
Principal investments, Direct \| Recurring \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	$ 1,000,000	$ 1,000,000

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=SL6742756-110258

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 35
-Paragraph 54B
-URI http://asc.fasb.org/extlink&oid=117332851&loc=SL7495116-110257

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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
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- Definition

Amount of impairment loss on investment in equity security without readily determinable fair value.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
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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.

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No definition available.

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Fair value of financial and nonfinancial obligations.

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-SubTopic 10
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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

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-Publisher FASB
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Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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