Securities - Investment Security Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Gross Realized Investment Gains	$ 2.4	$ 1.5	$ 0.2
Gross Realized Investment Losses	(3.5)	(2.0)	(1.6)
Other Than Temporary Impairment Losses	0.3	0.5	0.2
Investment Security Gains (Losses), net	$ (1.4)	$ (1.0)	$ (1.6)

Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

No definition available.

Name:	us-gaap_MarketableSecuritiesGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration