Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

The following table presents the effect of aggregate net EAC adjustments:



	Year Ended December 31
$ in millions, except per share data	2018		2017		2016
Operating income	$	577	$	360	$	443
Net earnings⁽¹⁾	456		234		288
Diluted earnings per share⁽¹⁾	2.61		1.33		1.60


⁽¹⁾	Based on statutory tax rates in effect for each year presented

Net contract assets (liabilities) are as follows:



$ in millions	December 31, 2018			December 31, 2017			$ Change			% Change
Unbilled receivables, net	$	5,026		$	3,465		$	1,561		45	%
Advance payments and amounts in excess of costs incurred	(1,917		)	(1,761		)	(156		)	9	%
Net contract assets (liabilities)	$	3,109		$	1,704		$	1,405		82	%

Major classes of property, plant and equipment and their useful lives are as follows:



		December 31
Useful life in years, $ in millions	Useful Life	2018			2017
Land and land improvements	Up to 40⁽¹⁾	$	636		$	420
Buildings and improvements	Up to 40	2,139			1,834
Machinery and other equipment	Up to 20	6,618			5,105
Capitalized software costs	3-5	603			537
Leasehold improvements	Length of Lease⁽²⁾	1,745			1,395
Property, plant and equipment, at cost		11,741			9,291
Accumulated depreciation		(5,369		)	(5,066		)
Property, plant and equipment, net		$	6,372		$	4,225


⁽¹⁾	Land is not a depreciable asset.


⁽²⁾	Leasehold improvements are depreciated over the shorter of the useful life of the asset or the length of the lease.

The components of accumulated other comprehensive (loss) income are as follows:



	December 31
$ in millions	2018			2017
Unamortized prior service credit, net of tax expense of $32 for 2018 and $76 for 2017	$	98		$	133
Cumulative translation adjustment	(144		)	(136		)
Other, net	(6		)	4
Total accumulated other comprehensive (loss) income	$	(52	)	$	1