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Shareholders' equity - Issued and Outstanding Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 7 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Jul. 31, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024
Class of Stock [Line Items] |  |  |  |  |  |
Preferred stock, shares issued (in shares) | 10,215,000 |  |  | 10,215,000 |  | 10,215,000
Preferred stock, shares outstanding (in shares) | 10,215,000 |  |  | 10,215,000 |  | 10,215,000
Carrying Amount | $ 2,394 |  |  | $ 2,394 |  | $ 2,394
Preferred Series E |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Preferred stock, shares issued (in shares) | 0 |  |  | 0 |  | 0
Preferred stock, shares outstanding (in shares) | 0 |  |  | 0 |  | 0
Preferred stock, liquidation preference per share (in USD per share) | $ 1,000 |  |  | $ 1,000 |  |
Preferred stock dividend rate (as a percent) |  |  |  | 0.00% |  |
Carrying Amount | $ 0 |  |  | $ 0 |  | $ 0
Preferred stock per share dividend amount (in USD per share) | $ 0 | $ 23.50 |  | $ 0 | $ 62.575 |
Preferred Series F |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Preferred stock, shares issued (in shares) | 50,000 |  |  | 50,000 |  | 50,000
Preferred stock, shares outstanding (in shares) | 50,000 |  |  | 50,000 |  | 50,000
Preferred stock, liquidation preference per share (in USD per share) | $ 10,000 |  |  | $ 10,000 |  |
Preferred stock dividend rate (as a percent) |  |  |  | 5.125% |  |
Carrying Amount | $ 500 |  |  | $ 500 |  | $ 500
Preferred stock per share dividend amount (in USD per share) | $ 128.125 | 128.125 |  | $ 384.375 | 384.375 |
Preferred stock. dividend rate spread (as a percent) |  |  |  | 3.78% |  |
Preferred Series G |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Preferred stock, shares issued (in shares) | 40,000 |  |  | 40,000 |  | 40,000
Preferred stock, shares outstanding (in shares) | 40,000 |  |  | 40,000 |  | 40,000
Preferred stock, liquidation preference per share (in USD per share) | $ 10,000 |  |  | $ 10,000 |  |
Preferred stock dividend rate (as a percent) |  |  | 5.00% | 7.304% |  |
Carrying Amount | $ 400 |  |  | $ 400 |  | $ 400
Preferred stock per share dividend amount (in USD per share) | $ 182.60 | 125.00 |  | $ 547.80 | 375.00 |
Preferred stock. dividend rate spread (as a percent) |  |  |  | 3.174% |  |
Preferred Series H |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Preferred stock, shares issued (in shares) | 10,000,000 |  |  | 10,000,000 |  | 10,000,000
Preferred stock, shares outstanding (in shares) | 10,000,000 |  |  | 10,000,000 |  | 10,000,000
Preferred stock, liquidation preference per share (in USD per share) | $ 25 |  |  | $ 25 |  |
Preferred stock dividend rate (as a percent) |  |  |  | 5.625% |  |
Carrying Amount | $ 261 |  |  | $ 261 |  | $ 261
Preferred stock per share dividend amount (in USD per share) | $ 0.3516 | 0.3516 |  | $ 1.0547 | 1.0547 |
Preferred stock. dividend rate spread (as a percent) |  |  |  | 4.28% |  |
Preferred Series I |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Preferred stock, shares issued (in shares) | 50,000 |  |  | 50,000 |  | 50,000
Preferred stock, shares outstanding (in shares) | 50,000 |  |  | 50,000 |  | 50,000
Preferred stock, liquidation preference per share (in USD per share) | $ 10,000 |  |  | $ 10,000 |  |
Preferred stock dividend rate (as a percent) |  |  |  | 3.50% |  |
Carrying Amount | $ 500 |  |  | $ 500 |  | $ 500
Preferred stock per share dividend amount (in USD per share) | $ 87.50 | 87.50 |  | $ 262.50 | 262.50 |
Preferred stock. dividend rate spread (as a percent) |  |  |  | 2.679% |  |
Preferred Series J |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Preferred stock, shares issued (in shares) | 75,000 |  |  | 75,000 |  | 75,000
Preferred stock, shares outstanding (in shares) | 75,000 |  |  | 75,000 |  | 75,000
Preferred stock, liquidation preference per share (in USD per share) | $ 10,000 |  |  | $ 10,000 |  |
Preferred stock dividend rate (as a percent) |  |  |  | 7.50% |  |
Carrying Amount | $ 733 |  |  | $ 733 |  | $ 733
Preferred stock per share dividend amount (in USD per share) | $ 187.50 | $ 254.17 |  | $ 562.50 | $ 254.17 |

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