Property and Casualty Insurance Reserves Historical Claims Duration (Details)	Dec. 31, 2017
Preferred Personal Automobile Liability Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	39.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	69.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	84.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	92.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	96.10%
Preferred Personal Automobile Physical Damage Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	98.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	100.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	100.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	100.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	100.10%
Non-standard Personal Automobile Liability Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	42.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	80.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	93.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	97.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	99.40%
Non-standard Personal Automobile Physical Damage Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	92.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	100.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	100.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	100.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	100.10%
Homeowners [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	70.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	94.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	97.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	98.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	98.70%