Securities Financing Agreements (Gross Obligations to Repurchase, Securities Loaned, and Class of Collateral Pledged) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	$ 33,911	$ 38,798
Securities loaned	495	93
Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	19,956	20,667
Securities loaned	259	93
Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	4,192	5,180
Securities loaned	236	0
31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	9,661	12,616
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, Gross	102	335
Securities loaned	0	0
US Treasury and Government [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	14,943	16,006
US Treasury and Government [Member] | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	12,219	9,680
US Treasury and Government [Member] | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	2,237	2,945
US Treasury and Government [Member] | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	385	3,046
US Treasury and Government [Member] | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	102	335
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	1,873	2,039
Securities loaned	2	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	688	682
Securities loaned	2	1
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	24	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, Gross	1,161	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, 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, Gross	860	879
Municipal bonds | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	327	115
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	0	245
Municipal bonds | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	533	519
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, Gross	2,205	862
Securities loaned	493	92
Equity securities | Maturity Overnight [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	1,400	387
Securities loaned	257	92
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	349	220
Securities loaned	236	0
Equity securities | 31-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	456	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, Gross	0	0
Securities loaned	0	0
U.S. government agency and government-sponsored agencies - residential mortgage-backed securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold under Agreements to Repurchase, Gross	14,030	19,012
U.S. government agency and government-sponsored agencies - residential 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	5,322	9,803
U.S. government agency and government-sponsored agencies - residential 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	1,582	1,640
U.S. government agency and government-sponsored agencies - residential 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	7,126	7,569
U.S. government agency and government-sponsored agencies - residential 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	$ 0