Preferred stock - Summary of Preferred Dividends Paid (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Class of Stock [Line Items]
Preferred dividends paid	$ 65	$ 32	$ 135	$ 103
Series A Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)	$ 1,178.1	$ 1,311.33	$ 2,283.28	$ 2,606.5
Preferred dividends paid	$ 6	$ 7	$ 12	$ 14
Series F Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)	$ 0	$ 0	$ 2,312.5	$ 2,312.5
Preferred dividends paid	$ 0	$ 0	$ 23	$ 23
Series G Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)		$ 0		$ 2,350
Preferred dividends paid		$ 0		$ 24
Series H Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)	$ 1,791.5	$ 925.00	$ 2,716.5	$ 1,850
Preferred dividends paid	$ 16	$ 5	$ 21	$ 10
Series I Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)	$ 937.50	$ 937.50	$ 1,875	$ 1,875
Preferred dividends paid	$ 12	$ 12	$ 24	$ 24
Series J Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)	$ 0		$ 3,150
Preferred dividends paid	$ 0		$ 16
Series K Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	0.03%		0.03%
Dividend paid per share (usd per share)	$ 1,537.5	$ 1,640	$ 3,075	$ 1,640
Preferred dividends paid	$ 8	$ 8	$ 16	$ 8
Series L Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)	$ 2,975		$ 2,975
Preferred dividends paid	$ 15		$ 15
Series M Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%		1.00%
Dividend paid per share (usd per share)	$ 1,640.63		$ 1,640.63
Preferred dividends paid	$ 8		$ 8