Reinsurance

We reinsure certain risks with other companies and assume risk from other companies. We remain primarily liable to policyholders under ceded insurance contracts and are contingently liable for amounts recoverable from reinsurers in the event that such reinsurers do not meet their contractual obligations. We evaluate the financial condition of our reinsurers and monitor concentrations of credit risk arising from similar geographic regions, activities, or economic characteristics of the reinsurers to minimize our exposure to significant losses from reinsurer insolvencies. In conjunction with the ACA temporary reinsurance premium stabilization program that was effective for 2014 through 2016, we recognized assessments upon our fully-insured non-grandfathered individual market plans that were eligible for reinsurance recoveries as ceded premiums and estimated reinsurance recoveries as a reduction to benefit expense. Assessments upon all other lines of business that were not eligible for reinsurance recoveries were recognized in general and administrative expense.

A summary of direct, assumed and ceded premiums written and earned for the years ended December 31, 2017, 2016 and 2015 is as follows:



	2017						2016						2015
	Written			Earned			Written			Earned			Written			Earned
Direct	$	83,974.3		$	83,417.8		$	78,200.4		$	78,726.2		$	72,925.5		$	73,259.2
Assumed	274.6			274.6			217.4			217.3			221.8			221.9
Ceded	(43.7		)	(44.7		)	(79.8		)	(83.4		)	(95.8		)	(96.0		)
Net premiums	$	84,205.2		$	83,647.7		$	78,338.0		$	78,860.1		$	73,051.5		$	73,385.1
Percentage—assumed to net premiums	0.3		%	0.3		%	0.3		%	0.3		%	0.3		%	0.3		%

A summary of net premiums written and earned by segment (see Note 19, “Segment Information”) for the years ended December 31, 2017, 2016 and 2015 is as follows:



	2017				2016				2015
	Written		Earned		Written		Earned		Written		Earned
Reportable segments:
Commercial & Specialty Business	$	35,683.1	$	35,804.3	$	33,355.6	$	33,831.5	$	33,016.9	$	33,078.0
Government Business	48,522.1		47,843.4		44,982.4		45,028.6		40,034.6		40,307.1
Net premiums	$	84,205.2	$	83,647.7	$	78,338.0	$	78,860.1	$	73,051.5	$	73,385.1

The effect of reinsurance on benefit expense for the years ended December 31, 2017, 2016 and 2015 is as follows:



	2017			2016			2015
Direct	$	72,135.0		$	67,221.7		$	61,674.0
Assumed	216.7			184.9			192.2
Ceded	(115.5		)	(572.2		)	(749.3		)
Net benefit expense	$	72,236.2		$	66,834.4		$	61,116.9

The effect of reinsurance on certain assets and liabilities at December 31, 2017 and 2016 is as follows:



	2017		2016
Policy liabilities, assumed	$	54.3	$	47.2
Unearned income, assumed	0.6		0.6
Premiums payable, ceded	9.3		5.2
Premiums receivable, assumed	32.9		25.9