Guarantee Arrangements, Pledged Assets and Repurchase Agreements, Collateral Pledged and Remaining Contractual Maturity of Repurchase Agreements Accounted for as Secured Borrowings (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	$ 4,435	$ 4,721
Maturity Overnight and Continuous [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	1,543	1,166
Maturity up to 30 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	829	919
Maturity 31 to 90 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	423	888
Maturity 91 Days to One Year [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	449	284
Maturity Greater than One Year [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	1,191	1,464
U.S. Treasury, U.S. Government agencies and sponsored entities [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	4,397	4,640
U.S. Treasury, U.S. Government agencies and sponsored entities [Member] | Maturity Overnight and Continuous [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	1,543	1,166
U.S. Treasury, U.S. Government agencies and sponsored entities [Member] | Maturity up to 30 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	791	838
U.S. Treasury, U.S. Government agencies and sponsored entities [Member] | Maturity 31 to 90 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	423	888
U.S. Treasury, U.S. Government agencies and sponsored entities [Member] | Maturity 91 Days to One Year [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	449	284
U.S. Treasury, U.S. Government agencies and sponsored entities [Member] | Maturity Greater than One Year [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	1,191	1,464
Foreign debt securities [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	38	81
Foreign debt securities [Member] | Maturity Overnight and Continuous [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	0	0
Foreign debt securities [Member] | Maturity up to 30 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	38	81
Foreign debt securities [Member] | Maturity 31 to 90 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	0	0
Foreign debt securities [Member] | Maturity 91 Days to One Year [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	0	0
Foreign debt securities [Member] | Maturity Greater than One Year [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	$ 0	$ 0