Securities - Net Impairment Losses Recognized In Earnings (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Changes in Other-Than-Temporary Impairment Losses	$ (0.5)	$ (0.2)	$ (3.7)
Noncredit-related Losses Recorded in / (Reclassified from) OCI	0.0	0.0	0.0
Net Impairment Losses Recognized in Earnings	$ (0.5)	$ (0.2)	$ (3.7)

Amount before tax of other than temporary impairment loss (OTTI) on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss and attributable to parent entity.

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