Goodwill and intangible assets - Intangible Assets by Type (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Intangible Assets by Major Class [Line Items]
Gross carrying amount	$ 4,863	$ 4,881
Accumulated amortization	(1,793)	(1,774)
Net carrying amount	3,070	3,107	$ 3,193	$ 3,220
Finite-lived Intangible Assets
Intangible Assets by Major Class [Line Items]
Gross carrying amount	2,288	2,296
Accumulated amortization	(1,793)	(1,774)
Net carrying amount	$ 495	522
Finite-lived Intangible Assets | Weighted Average
Intangible Assets by Major Class [Line Items]
Remaining weighted- average amortization period	10 years
Finite-lived Intangible Assets | Customer contracts—Investment Services
Intangible Assets by Major Class [Line Items]
Gross carrying amount	$ 1,515	1,520
Accumulated amortization	(1,227)	(1,214)
Net carrying amount	$ 288	306
Finite-lived Intangible Assets | Customer contracts—Investment Services | Weighted Average
Intangible Assets by Major Class [Line Items]
Remaining weighted- average amortization period	10 years
Finite-lived Intangible Assets | Customer relationships
Intangible Assets by Major Class [Line Items]
Gross carrying amount	$ 709	712
Accumulated amortization	(548)	(544)
Net carrying amount	$ 161	168
Finite-lived Intangible Assets | Customer relationships | Weighted Average
Intangible Assets by Major Class [Line Items]
Remaining weighted- average amortization period	11 years
Finite-lived Intangible Assets | Other
Intangible Assets by Major Class [Line Items]
Gross carrying amount	$ 64	64
Accumulated amortization	(18)	(16)
Net carrying amount	$ 46	48
Finite-lived Intangible Assets | Other | Weighted Average
Intangible Assets by Major Class [Line Items]
Remaining weighted- average amortization period	14 years
Indefinite-lived Intangible Assets
Intangible Assets by Major Class [Line Items]
Gross carrying amount	$ 2,575	2,585
Net carrying amount	2,575	2,585
Indefinite-lived Intangible Assets | Tradenames
Intangible Assets by Major Class [Line Items]
Gross carrying amount	1,291	1,293
Net carrying amount	1,291	1,293
Indefinite-lived Intangible Assets | Customer relationships
Intangible Assets by Major Class [Line Items]
Gross carrying amount	1,284	1,292
Net carrying amount	$ 1,284	$ 1,292