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