Securities Financing Agreements (Gross Obligations to Repurchase, Securities Loaned, and Class of Collateral Pledged) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	$ 38,891	$ 37,388
Securities sold under agreements to repurchase	27,285	26,437
Securities loaned	93	879
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities loaned	93	446
Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities loaned	0	332
31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities loaned	0	101
Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities loaned	0	0
U.S. Treasury
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	15,687	12,818
Securities loaned		322
U.S. Treasury | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	9,416
U.S. Treasury | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross		8,244
U.S. Treasury | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	2,945	2,370
U.S. Treasury | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	2,991	1,046
U.S. Treasury | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	335	1,158
U.S. government-sponsored agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	319	216
U.S. government-sponsored agencies | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	264
U.S. government-sponsored agencies | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross		115
U.S. government-sponsored agencies | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	0	38
U.S. government-sponsored agencies | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	55	63
U.S. government-sponsored agencies | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	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, Gross		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, Gross		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, Gross		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, Gross		0
Money market funds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	49	7
Money market funds | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	0	1
Money market funds | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	0	0
Money market funds | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	49	6
Money market funds | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	0	0
Asset-backed securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	282	196
Asset-backed securities | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	0
Asset-backed securities | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross		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, Gross	0	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, Gross	282	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, Gross	0	0
Mortgage-backed securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	19,012	19,403
Mortgage-backed securities | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	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, Gross		8,322
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, Gross	1,640	4,972
Mortgage-backed securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	7,569	5,859
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, Gross	0	250
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	2,039	2,325
Securities loaned	1
Corporate bonds | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	682
Corporate bonds | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross		580
Securities loaned	1	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, Gross	130	620
Securities loaned	0	322
Corporate bonds | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	1,227	1,125
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, Gross	0	0
Securities loaned	0	0
Municipal bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	548	559
Municipal bonds | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	115
Municipal bonds | Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross		283
Municipal bonds | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	245	0
Municipal bonds | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	188	276
Municipal bonds | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	0	0
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities sold under agreements to repurchase	862	981
Securities loaned	92	557
Equity securities | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	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, Gross		416
Securities loaned		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, Gross	220	376
Securities loaned	0	10
Equity securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	255	189
Securities loaned	0	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, Gross	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	38,798	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	20,667	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	5,180	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	12,616	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	$ 335	$ 1,408