Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,098,000,000.0	$ 2,844,000,000.0
Gross Amounts Offset in the Balance Sheet	1,408,300,000	2,338,000,000.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	689,700,000	506,000,000.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	29,700,000	16,500,000
Net Amount	660,000,000.0	489,500,000
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	515,200,000	543,700,000
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	900,000	300,000
Net Amount	514,300,000	543,400,000
Total Derivatives
GROSS RECOGNIZED ASSETS	2,613,200,000	3,387,700,000
Derivative Assets	1,204,900,000	1,049,700,000
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	30,600,000	16,800,000
Net Amount	1,174,300,000	1,032,900,000
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	1,533,400,000	707,800,000
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1,533,400,000	707,800,000
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1,533,400,000	707,800,000
Other assets excluding derivatives and non financial instruments	7,300,000,000	7,400,000,000
Federal funds sold	0	5,000,000.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	1,764,300,000	2,691,100,000
Gross Amounts Offset in the Balance Sheet	1,405,700,000	2,334,100,000
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	358,600,000	357,000,000.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	29,700,000	16,500,000
Net Amount	328,900,000	340,500,000
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	333,700,000	151,900,000
Gross Amounts Offset in the Balance Sheet	2,600,000	3,900,000
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	331,100,000	148,000,000.0
Net Amount	$ 331,100,000	148,000,000.0
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		1,000,000.0
Gross Amounts Offset in the Balance Sheet		0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		1,000,000.0
Net Amount		$ 1,000,000.0