Preferred stock - Summary (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Total shares issued and outstanding (shares)	48,826	48,826
Carrying value	$ 4,838	$ 4,838
Series A Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	4.00%
Total shares issued and outstanding (shares)	5,001	5,001
Carrying value	$ 500	$ 500
Liquidation preference per share (usd per share)	$ 100,000
Depositary shares per share	1.00%
Series A Noncumulative Perpetual Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate	0.565%
Series D Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	4.50%
Total shares issued and outstanding (shares)	5,000	5,000
Carrying value	$ 494	$ 494
Liquidation preference per share (usd per share)	$ 100,000
Depositary shares per share	1.00%
Series D Noncumulative Perpetual Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate	2.46%
Series F Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	4.625%
Total shares issued and outstanding (shares)	10,000	10,000
Carrying value	$ 990	$ 990
Liquidation preference per share (usd per share)	$ 100,000
Depositary shares per share	1.00%
Series F Noncumulative Perpetual Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate	3.131%
Series G Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	4.70%
Total shares issued and outstanding (shares)	10,000	10,000
Carrying value	$ 990	$ 990
Liquidation preference per share (usd per share)	$ 100,000
Depositary shares per share	1.00%
Series G Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate	4.358%
Series H Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	3.70%
Total shares issued and outstanding (shares)	5,825	5,825
Carrying value	$ 577	$ 577
Liquidation preference per share (usd per share)	$ 100,000
Depositary shares per share	1.00%
Series H Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate	3.352%
Series I Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	3.75%
Total shares issued and outstanding (shares)	13,000	13,000
Carrying value	$ 1,287	$ 1,287
Liquidation preference per share (usd per share)	$ 100,000
Depositary shares per share	1.00%
Series I Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate	2.63%
Series E Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Depositary shares per share	1.00%