Goodwill and intangible assets - Intangible Assets by Business Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Intangible Assets [Roll Forward]
Beginning Balance	$ 3,107		$ 3,220
Amortization	(26)	$ (28)	(29)
Foreign currency translation	(11)		2
Ending Balance	3,070	3,107	3,193
Investment Services
Intangible Assets [Roll Forward]
Beginning Balance	678		758
Amortization	(18)		(20)
Foreign currency translation	(1)		(1)
Ending Balance	659	678	737
Investment Management
Intangible Assets [Roll Forward]
Beginning Balance	1,580		1,613
Amortization	(8)		(9)
Foreign currency translation	(10)		3
Ending Balance	1,562	1,580	1,607
Other
Intangible Assets [Roll Forward]
Beginning Balance	849		849
Amortization	0		0
Foreign currency translation	0		0
Ending Balance	$ 849	$ 849	$ 849