In the normal course of business, the Company purchases treaty and facultative reinsurance protection to limit its ultimate losses from catastrophic events and reduce its loss aggregation risk.

Facultative reinsurance provides cover for all or a portion of the losses incurred for a single policy and the Company separately negotiates each facultative contract.

Treaty reinsurance provides cover for a specified type or category of risks. The Company's treaty reinsurance agreements provide this cover on either an excess of loss or a proportional basis. Excess of loss covers provide a contractually set amount of coverage after a specified loss amount has been reached. These treaties can provide cover for a number of lines of business within one contract. Under proportional reinsurance, the Company cedes an agreed proportion of the premiums and the losses and loss expenses on the policies it underwrites. These treaties provide us with a specified percentage of coverage from the first dollar of loss.

All of these reinsurance covers provide the Company the right to recover a portion of specified losses and loss expenses from reinsurers. However, to the extent that reinsurers do not meet their obligations under these agreements due to solvency issues, contractual disputes or other reasons, the Company remains liable. The Company predominantly cedes its business to reinsurers rated A- or better by internationally recognized rating agencies.

Gross and net premiums written and earned were as follows:




Year ended December 31,	2018						2017						2016
	Premiums written			Premiums earned			Premiums written			Premiums earned			Premiums written			Premiums earned

Gross	$	6,910,065		$	6,882,217		$	5,556,273		$	5,616,234		$	4,970,208		$	4,762,394
Ceded	(2,251,103		)	(2,090,722		)	(1,529,130		)	(1,467,474		)	(1,217,234		)	(1,056,769		)
Net	$	4,658,962		$	4,791,495		$	4,027,143		$	4,148,760		$	3,752,974		$	3,705,625

For the year ended December 31, 2018, the Company recognized ceded losses and loss expenses of $1,565 million (2017: $1,010 million; 2016: $556 million).

At December 31, 2018, the Company's provision for uncollectible amounts was $21 million (2017: $17 million; 2016: $20 million).