Property and Casualty Insurance Reserves Historical Claims Duration (Details)	Dec. 31, 2016
Preferred Personal Automobile Liability Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	41.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	72.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	85.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	93.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	96.70%
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	98.90%
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	100.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	100.00%
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	44.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	81.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	93.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	97.90%
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	92.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	100.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	100.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	99.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	100.00%
Homeowners [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	72.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	94.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	97.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	98.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	99.60%