Other assets - Qualified Affordable Housing Project Investments (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Other Assets [Abstract]
Qualified affordable housing project investments	$ 997			$ 997		$ 1,024
Qualified affordable housing project investments, commitment	388			388		$ 422
Qualified affordable housing project commitment - 2020	40			40
Qualified affordable housing project commitment - 2021	187			187
Qualified affordable housing project commitment - 2022	99			99
Qualified affordable housing project commitment - 2023	36			36
Qualified affordable housing project commitment - 2024	1			1
Qualified affordable housing project commitment - 2025 and thereafter	25			25
Tax credits and other tax benefits	35	$ 38	$ 39	111	$ 117
Amortization expense included in the provision for income taxes	$ 30	$ 31	$ 33	$ 92	$ 97