Preferred stock - Summary of Preferred Dividends Paid (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Class of Stock [Line Items]
Preferred dividends paid	$ 34	$ 74	$ 31	$ 108	$ 100
Series A Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%			1.00%
Dividend paid per share (usd per share)	$ 1,022.22	$ 1,011.11	$ 1,011.11	$ 2,033.33	$ 2,022.22
Preferred dividends paid	$ 5	$ 5	$ 5	$ 10	$ 10
Series D Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%			1.00%
Dividend paid per share (usd per share)	$ 2,250		$ 2,250	$ 2,250	$ 2,250
Preferred dividends paid	$ 11		$ 11	$ 11	$ 11
Series E Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%			1.00%
Dividend paid per share (usd per share)			$ 911.68		$ 1,836.5
Preferred dividends paid			$ 9		$ 18
Series F Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%			1.00%
Dividend paid per share (usd per share)		$ 2,312.5		$ 2,312.5	$ 2,312.5
Preferred dividends paid		$ 23		$ 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)		$ 2,350		$ 2,350	$ 2,350
Preferred dividends paid		$ 24		$ 24	$ 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)	$ 925.00	$ 925.00	$ 925.00	$ 1,850	$ 2,333.06
Preferred dividends paid	$ 6	$ 5	$ 6	$ 11	$ 14
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	$ 1,270.83		$ 2,208.33
Preferred dividends paid	$ 12	$ 17		$ 29