Liability for Unpaid Claims and Claims Adjustment Expenses Liability for Unpaid Claims - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Liability for Claims and Claims Adjustment Expense - Narrative
Long-term Care Reserve Increase, Before Tax	$ 750.8
Long-term Care Reserve Increase, After Tax	593.1
Claim Reserve
Liability for Claims and Claims Adjustment Expense - Narrative
Long-term Care Reserve Increase, After Tax	$ 236.0