Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other equity investments	$ 147,000,000		$ 134,000,000
Impairment loss (less than)	1,000,000
Discontinued operations | Education Lending
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans at fair value	2,000,000	$ 2,000,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	655,000,000	605,000,000
Loans at fair value	5,000,000	4,000,000
Fair Value | Discontinued operations | Education Lending
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	608,000,000	729,000,000
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	655,000,000	605,000,000
Loans at fair value	5,000,000	4,000,000
Carrying Amount | Discontinued operations | Education Lending
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	737,000,000	855,000,000
Level 3 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	590,000,000	528,000,000
Loans at fair value	5,000,000	4,000,000
Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	78,000,000	90,000,000
Liabilities measured at fair value on non recurring basis	1,025,000,000	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	20,000,000	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