In the ordinary course of business, we purchase treaty and facultative reinsurance to reduce exposure to significant losses. Facultative reinsurance provides coverage for all or a portion of the losses incurred for a single policy and we separately negotiate each facultative contract. Treaty reinsurance provides coverage for a specified type or category of risks. Our treaty reinsurance agreements provide this coverage 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. Under proportional reinsurance, we cede an agreed proportion of the premiums and the losses and loss adjustment expenses on the policies we underwrite. Treaty reinsurance can provide us with coverage for a number of lines of business within one contract. In contrast, proportional covers provide us with a specified percentage of coverage from the first dollar of loss.

All of these reinsurance covers provide us the right to recover a portion of specified losses and loss expenses from reinsurers. However, to the extent that our reinsurers do not meet their obligations under these agreements due to solvency issues, contractual disputes or other reasons, we remain liable. We predominantly cede our business to reinsurers rated A- or better by A.M. Best.

Gross and net premiums written and earned were as follows:




Year ended December 31,	2016						2015						2014
	Premiums written			Premiums earned			Premiums written			Premiums earned			Premiums written			Premiums earned

Gross	$	4,970,208		$	4,762,394		$	4,603,730		$	4,567,953		$	4,711,519		$	4,652,345
Ceded	(1,217,234		)	(1,056,769		)	(929,064		)	(881,536		)	(804,544		)	(781,346		)
Net	$	3,752,974		$	3,705,625		$	3,674,666		$	3,686,417		$	3,906,975		$	3,870,999

During the year ended December 31, 2016, we recognized ceded losses and loss expenses of $556 million (2015: $577 million; 2014: $401 million).

Our provision for unrecoverable reinsurance was $20 million at December 31, 2016 (2015: $18 million). At December 31, 2016, 96.7% (2015: 96.2%) of our gross reinsurance recoverables were collectible from reinsurers rated A- or better by A.M. Best.