Other assets - Qualified Affordable Housing Project Investments (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Other Assets [Abstract]
Qualified affordable housing project investments	$ 962			$ 962		$ 1,024
Qualified affordable housing project investments, commitment	363			363		$ 422
Qualified affordable housing project commitment - 2020	72			72
Qualified affordable housing project commitment - 2021	179			179
Qualified affordable housing project commitment - 2022	82			82
Qualified affordable housing project commitment - 2023	5			5
Qualified affordable housing project commitment - 2024	1			1
Qualified affordable housing project commitment - 2025 and thereafter	24			24
Tax credits and other tax benefits	38	$ 38	$ 39	76	$ 78
Amortization expense included in the provision for income taxes	$ 31	$ 31	$ 32	$ 62	$ 64