Commitments, contingencies, and guarantees Commitments, contingencies, and guarantees (Collateral pledged under repurchase agreements) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	$ 1,461	$ 1,459
Securities Sold under Agreements to Repurchase	1,403	1,404
Cash and Cash Equivalents [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	1	34
US Treasury and Government [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	240	237
Mortgage backed-securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	1,220	1,188
Repurchase Agreements [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Secured Borrowings, Gross, Difference, Amount	58	55
Maturity Greater than 90 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	892	574
Maturity Greater than 90 Days [Member] \| Cash and Cash Equivalents [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	1	0
Maturity Greater than 90 Days [Member] \| US Treasury and Government [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	10	231
Maturity Greater than 90 Days [Member] \| Mortgage backed-securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	881	343
Maturity Less than 30 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	569	405
Maturity Less than 30 Days [Member] \| Cash and Cash Equivalents [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	0	34
Maturity Less than 30 Days [Member] \| US Treasury and Government [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	230	6
Maturity Less than 30 Days [Member] \| Mortgage backed-securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	$ 339	365
Maturity 30 to 90 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements		480
Maturity 30 to 90 Days [Member] \| Cash and Cash Equivalents [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements		0
Maturity 30 to 90 Days [Member] \| US Treasury and Government [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements		0
Maturity 30 to 90 Days [Member] \| Mortgage backed-securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements		$ 480

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

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- Definition

Amount of secured borrowings in excess of (less than) the liability for repurchase agreements and securities lending transactions, before offset, included in offsetting disclosures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 7
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL34722452-111729

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(a)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(1))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=49176635&loc=d3e9760-107771

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Repurchase Agreement Accounted for as a Collateralized Borrowing
-URI http://asc.fasb.org/extlink&oid=49203159

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+ References

No definition available.

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