Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions |
Jun. 30, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Significant Accounting Policies [Line Items] | ||
| Operating lease liability | $ 754 | |
| Fair value of loaned securities | 17,000 | $ 18,900 |
| Fair value of collateral held for loan securities | $ 18,446 | $ 20,655 |
| Minimum [Member] | ||
| Significant Accounting Policies [Line Items] | ||
| Collateral cash and securities received in exchange of value of securities lent in order to reduce counterparty risk | 102.00% | |
| Maximum [Member] | ||
| Significant Accounting Policies [Line Items] | ||
| Collateral cash and securities received in exchange of value of securities lent in order to reduce counterparty risk | 112.00% | |
| Accounting Standards Update 2016-02 [Member] | ||
| Significant Accounting Policies [Line Items] | ||
| Operating lease liability | $ 700 |