Parent Company - Additional Information (Detail) - Group Inc. [Member] - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Parent Company Only Financial Information [Line Items] | |||
| Noncash or Part Noncash Acquisition, Debt Assumed | $ 8,500.0 | ||
| Net increase in loans to subsidiaries which resulted from restructured funding | $ 5,710.0 | ||
| Decrease in equity interest which resulted from restructured funding | 5,710.0 | ||
| Liabilities exchanged for equity interest in subsidiary | 150.0 | ||
| Deferred tax assets exchanged for equity interest in subsidiary | 46.0 | ||
| Equity interest in subsidiary received in exchange for liabilities and deferred tax assets | 104.0 | ||
| Trust Preferred Securities and common beneficial interests exchanged with the firm's junior subordinated debt | $ 11.2 | 211.0 | 36.0 |
| Firm's Junior subordinated debt exchanged for Trust Preferred Securities and common beneficial interests | $ 12.5 | $ 231.0 | $ 36.0 |