Other assets - Qualified Affordable Housing Project Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Other Assets [Abstract]
Qualified affordable housing project investments	$ 993	$ 1,024
Qualified affordable housing project investments, commitment	390	422
Qualified affordable housing project commitment - 2020	114
Qualified affordable housing project commitment - 2021	181
Qualified affordable housing project commitment - 2022	83
Qualified affordable housing project commitment - 2023	6
Qualified affordable housing project commitment - 2024	2
Qualified affordable housing project commitment - 2025 and thereafter	4
Tax credits and other tax benefits	38	31	$ 39
Amortization expense included in the provision for income taxes	$ 31	$ 24	$ 32