Capital Stock - Additional Information (Detail) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Mar. 25, 2019 |
Jan. 31, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
|
| Schedule of Capitalization, Equity [Line Items] | |||||
| Common shares repurchased | 3,800,000 | ||||
| Common shares repurchased, value | $ 300 | $ 1,566 | $ 635 | ||
| Shares authorized to be repurchased | 6,100,000 | ||||
| Series C Nonvoting Participating Preferred Stock [Member] | PNC [Member] | |||||
| Schedule of Capitalization, Equity [Line Items] | |||||
| Surrender of share of series non- voting preferred stock | 143,458 | ||||
| Private Transaction | |||||
| Schedule of Capitalization, Equity [Line Items] | |||||
| Common shares repurchased, value | $ 1,300 | ||||