Securities Financing Arrangements - Secured Borrowings by Contractual Maturity and Class of Collateral Pledged (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	$ 38,254	$ 37,388
Securities loaned	1,064	879
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	22,280
Securities loaned	672	446
Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	4,391
Securities loaned	346	332
31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	9,404
Securities loaned	46	101
Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	1,115
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	13,793	12,818
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	11,769	8,244
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	250	2,370
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	1,409	1,046
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	365	1,158
U.S. government-sponsored agency securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	92	216
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	92	115
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	0	38
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	0	63
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		4
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		4
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	28	7
Money market securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	2	1
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	26	6
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		196
Asset-backed securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		32
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		164
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	19,965	19,403
Securities loaned	219
Mortgage-backed securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	9,011	8,322
Securities loaned	0
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	3,872	4,972
Securities loaned	219
Mortgage-backed securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	6,332	5,859
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	750	250
Securities loaned	0
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	2,320	2,325
Securities loaned		322
Corporate bonds | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	1,044	580
Securities loaned		0
Corporate bonds | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	142	620
Securities loaned		322
Corporate bonds | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	1,134	1,125
Securities loaned		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
State and municipal securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	534	559
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	249	283
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	21	0
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	264	276
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	458	981
Securities loaned	845	557
Equity securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	113	416
Securities loaned	672	446
Equity securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	106	376
Securities loaned	127	10
Equity securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	239	189
Securities loaned	46	101
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	$ 37,190	36,509
Trading securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		17,993
Trading securities | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		8,376
Trading securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		8,732
Trading securities | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase		$ 1,408