Investment securities (Investments Classified by Credit Rating) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 1,170	$ 1,253
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,170	1,253
AA Rating
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,170	1,253
AA Rating \| Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 1,170	$ 1,253

Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Name:	us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant