Securities Financing Arrangements - Secured Borrowings by Contractual Maturity and Class of Collateral Pledged (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	$ 36,679	$ 38,891
Securities loaned	694	93
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	18,109
Securities loaned	443	93
Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	6,288
Securities loaned	251	0
31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	10,154
Securities loaned	0	0
Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	1,434
Securities loaned	0	0
U.S. Treasury securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	16,396	15,687
U.S. Treasury securities | Maturity Overnight and on Demand [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		9,416
U.S. Treasury securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	9,996
U.S. Treasury securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	3,726	2,945
U.S. Treasury securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	1,840	2,991
U.S. Treasury securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	834	335
U.S. government-sponsored agency securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	142	319
U.S. government-sponsored agency securities | Maturity Overnight and on Demand [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		264
U.S. government-sponsored agency securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	99
U.S. government-sponsored agency securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	2	0
U.S. government-sponsored agency securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	41	55
U.S. government-sponsored agency securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	0
Other sovereign government obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	3
Other sovereign government obligations | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0
Other sovereign government obligations | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0
Other sovereign government obligations | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	3
Other sovereign government obligations | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0
Money market securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	307	49
Money market securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	0
Money market securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	0
Money market securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	307	49
Money market securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	0
Asset-backed securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		282
Asset-backed securities | Maturity Overnight and on Demand [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		0
Asset-backed securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		0
Asset-backed securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		282
Asset-backed securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		0
Mortgage-backed securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	15,651	19,012
Securities loaned	151
Mortgage-backed securities | Maturity Overnight and on Demand [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		9,803
Mortgage-backed securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	5,919
Securities loaned	151
Mortgage-backed securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	2,510	1,640
Securities loaned	0
Mortgage-backed securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	6,622	7,569
Securities loaned	0
Mortgage-backed securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	600	0
Securities loaned	0
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	2,365	2,039
Securities loaned	10	1
Corporate bonds | Maturity Overnight and on Demand [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		682
Securities loaned		1
Corporate bonds | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	1,285
Securities loaned	10
Corporate bonds | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	43	130
Securities loaned	0	0
Corporate bonds | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	1,037	1,227
Securities loaned	0	0
Corporate bonds | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	0
Securities loaned	0	0
State and municipal securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	551	548
State and municipal securities | Maturity Overnight and on Demand [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		115
State and municipal securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	503
State and municipal securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	245
State and municipal securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	48	188
State and municipal securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	0
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	570	862
Securities loaned	533	92
Equity securities | Maturity Overnight and on Demand [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		387
Securities loaned		92
Equity securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	307
Securities loaned	282
Equity securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	7	220
Securities loaned	251	0
Equity securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	256	255
Securities loaned	0	0
Equity securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	0	0
Securities loaned	0	0
Trading securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	$ 35,985	38,798
Trading securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		20,667
Trading securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		5,180
Trading securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		12,616
Trading securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		$ 335