Earnings per common share - Computations of Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Earnings Per Share [Abstract]
Net income available to common equity	$ 756	$ 674	$ 1,985	$ 1,808
Less: Income attributable to unvested stock-based compensation awards	(2)	0	(4)	(3)
Net income available to common shareholders	$ 754	$ 674	$ 1,981	$ 1,805
Adjusted weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards (in shares)	155,885	167,011	159,956	167,010
Less: Unvested stock-based compensation awards (in shares)	(327)	(340)	(325)	(316)
Plus: Incremental shares from assumed conversion of stock-based compensation awards (in shares)	995	896	872	743
Adjusted weighted-average shares outstanding (in shares)	156,553	167,567	160,503	167,437
Diluted earnings per common share (in USD per share)	$ 4.82	$ 4.02	$ 12.34	$ 10.78