Unpaid Loss and Loss Adjustment Expenses Average historical claims duration (Details)	Dec. 31, 2018
Year One [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	59.60%
Year Two [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	22.10%
Year Three [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	10.70%
Year Four [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	5.20%
Year Five [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	2.00%
Year Six [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.40%
Year Seven [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%
Year Eight [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%
Year Nine [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%
Year Ten [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%
Commercial auto liability [Member] | Year One [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	70.30%
Commercial auto liability [Member] | Year Two [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	9.70%
Commercial auto liability [Member] | Year Three [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	8.90%
Commercial auto liability [Member] | Year Four [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	7.40%
Commercial auto liability [Member] | Year Five [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	3.00%
Commercial auto liability [Member] | Year Six [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.70%
Commercial auto liability [Member] | Year Seven [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%
Commercial auto liability [Member] | Year Eight [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%
Commercial auto liability [Member] | Year Nine [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%
Commercial auto liability [Member] | Year Ten [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	0.00%