Other assets - Qualified Affordable Housing Project Investments (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Other Assets [Abstract]
Qualified affordable housing project investments	$ 1,104			$ 1,104		$ 1,145
Qualified affordable housing project investments, commitment	480			480		$ 514
Qualified affordable housing project commitment - 2021	77			77
Qualified affordable housing project commitment - 2022	163			163
Qualified affordable housing project commitment - 2023	162			162
Qualified affordable housing project commitment - 2024	58			58
Qualified affordable housing project commitment - 2025	2			2
Qualified affordable housing project commitment - 2026 and thereafter	18			18
Tax credits and other tax benefits	38	$ 38	$ 35	114	$ 111
Amortization expense included in the provision for income taxes	$ 32	$ 32	$ 30	$ 96	$ 92