LIABILITY FOR LOSSES AND SETTLEMENT EXPENSES HISTORICAL CLAIMS DURATION (Details)	Dec. 31, 2017
Commercial Auto Liability [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	23.50%
Short-duration insurance contracts, historical claims duration, year two	25.70%
Short-duration insurance contracts, historical claims duration, year three	21.20%
Short-duration insurance contracts, historical claims duration, year four	15.40%
Short-duration insurance contracts, historical claims duration, year five	8.00%
Short-duration insurance contracts, historical claims duration, year six	3.20%
Short-duration insurance contracts, historical claims duration, year seven	1.20%
Short-duration insurance contracts, historical claims duration, year eight	0.30%
Short-duration insurance contracts, historical claims duration, year nine	0.30%
Short-duration insurance contracts, historical claims duration, year ten	0.00%
Commercial Property [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	70.30%
Short-duration insurance contracts, historical claims duration, year two	20.10%
Short-duration insurance contracts, historical claims duration, year three	4.00%
Short-duration insurance contracts, historical claims duration, year four	1.90%
Short-duration insurance contracts, historical claims duration, year five	1.70%
Short-duration insurance contracts, historical claims duration, year six	0.80%
Short-duration insurance contracts, historical claims duration, year seven	0.30%
Short-duration insurance contracts, historical claims duration, year eight	0.10%
Short-duration insurance contracts, historical claims duration, year nine	0.50%
Short-duration insurance contracts, historical claims duration, year ten	0.00%
Workers' Compensation [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	30.50%
Short-duration insurance contracts, historical claims duration, year two	29.80%
Short-duration insurance contracts, historical claims duration, year three	13.80%
Short-duration insurance contracts, historical claims duration, year four	7.20%
Short-duration insurance contracts, historical claims duration, year five	4.20%
Short-duration insurance contracts, historical claims duration, year six	2.50%
Short-duration insurance contracts, historical claims duration, year seven	1.80%
Short-duration insurance contracts, historical claims duration, year eight	1.30%
Short-duration insurance contracts, historical claims duration, year nine	0.90%
Short-duration insurance contracts, historical claims duration, year ten	0.90%
Other Liability [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	11.50%
Short-duration insurance contracts, historical claims duration, year two	19.60%
Short-duration insurance contracts, historical claims duration, year three	19.50%
Short-duration insurance contracts, historical claims duration, year four	17.20%
Short-duration insurance contracts, historical claims duration, year five	12.70%
Short-duration insurance contracts, historical claims duration, year six	7.30%
Short-duration insurance contracts, historical claims duration, year seven	3.50%
Short-duration insurance contracts, historical claims duration, year eight	1.90%
Short-duration insurance contracts, historical claims duration, year nine	1.00%
Short-duration insurance contracts, historical claims duration, year ten	0.80%
Personal Auto Liability [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	29.40%
Short-duration insurance contracts, historical claims duration, year three	14.90%
Short-duration insurance contracts, historical claims duration, year four	8.20%
Short-duration insurance contracts, historical claims duration, year five	2.60%
Short-duration insurance contracts, historical claims duration, year six	1.80%
Short-duration insurance contracts, historical claims duration, year seven	0.70%
Short-duration insurance contracts, historical claims duration, year eight	0.30%
Short-duration insurance contracts, historical claims duration, year nine	0.20%
Short-duration insurance contracts, historical claims duration, year ten	0.00%
Homeowners Insurance [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	82.20%
Short-duration insurance contracts, historical claims duration, year two	14.90%
Short-duration insurance contracts, historical claims duration, year three	1.70%
Short-duration insurance contracts, historical claims duration, year four	0.90%
Short-duration insurance contracts, historical claims duration, year five	0.50%
Short-duration insurance contracts, historical claims duration, year six	0.10%
Short-duration insurance contracts, historical claims duration, year seven	0.20%
Short-duration insurance contracts, historical claims duration, year eight	0.10%
Short-duration insurance contracts, historical claims duration, year nine	0.00%
Short-duration insurance contracts, historical claims duration, year ten	0.00%
Auto Physical Damage [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	94.30%
Short-duration insurance contracts, historical claims duration, year two	6.60%
Short-duration insurance contracts, historical claims duration, year three	(0.30%)
Short-duration insurance contracts, historical claims duration, year four	(0.10%)
Short-duration insurance contracts, historical claims duration, year five	(0.10%)
Short-duration insurance contracts, historical claims duration, year six	0.00%
Short-duration insurance contracts, historical claims duration, year seven	0.00%
Short-duration insurance contracts, historical claims duration, year eight	0.00%
Short-duration insurance contracts, historical claims duration, year nine	0.00%
Short-duration insurance contracts, historical claims duration, year ten	0.00%
Assumed Pro Rata [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	28.40%
Short-duration insurance contracts, historical claims duration, year two	39.50%
Short-duration insurance contracts, historical claims duration, year three	15.00%
Short-duration insurance contracts, historical claims duration, year four	6.50%
Short-duration insurance contracts, historical claims duration, year five	2.70%
Short-duration insurance contracts, historical claims duration, year six	0.90%
Short-duration insurance contracts, historical claims duration, year seven	0.60%
Short-duration insurance contracts, historical claims duration, year eight	0.90%
Short-duration insurance contracts, historical claims duration, year nine	0.60%
Short-duration insurance contracts, historical claims duration, year ten	0.30%
Assumed Excess of Loss [Member]
Short-duration insurance contracts, historical claims duration [Line Items]
Short-duration insurance contracts, historical claims duration, year one	32.30%
Short-duration insurance contracts, historical claims duration, year two	31.20%
Short-duration insurance contracts, historical claims duration, year three	10.30%
Short-duration insurance contracts, historical claims duration, year four	6.70%
Short-duration insurance contracts, historical claims duration, year five	3.30%
Short-duration insurance contracts, historical claims duration, year six	2.50%
Short-duration insurance contracts, historical claims duration, year seven	2.10%
Short-duration insurance contracts, historical claims duration, year eight	0.80%
Short-duration insurance contracts, historical claims duration, year nine	1.10%
Short-duration insurance contracts, historical claims duration, year ten	0.50%