Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase (Tables)

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Securities Purchased under Agreements to Resell

($ In Millions)	2018			2017
Balance at December 31	$	1,031.2		$	1,303.3
Average Balance During the Year	1,478.3			1,832.0
Average Interest Rate Earned During the Year	2.22		%	1.48		%
Maximum Month-End Balance During the Year	1,942.0			2,064.1

Securities Sold under Agreements to Repurchase

($ In Millions)	2018			2017
Balance at December 31	$	168.3		$	834.0
Average Balance During the Year	525.2			738.9
Average Interest Rate Paid During the Year	1.48		%	0.81		%
Maximum Month-End Balance During the Year	981.3			834.0

Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Table Text Block]

	December 31, 2018
(In Millions)	Remaining Contractual Maturity of the Agreements
Repurchase Agreements	Overnight and Continuous
U.S. Treasury and Agency Securities	$	168.3
Total Borrowings	168.3
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 27	168.3
Amounts related to agreements not included in Note 27	—