Retirement Benefits (Unaudited) (Tables)

6 Months Ended

Jun. 30, 2018

Retirement Benefits [Abstract]

Components of net periodic benefit cost

The cost to the company of its retirement plans is shown in the following table:

	Three Months Ended June 30												Six Months Ended June 30
	Pension Benefits						Medical and Life Benefits						Pension Benefits						Medical and Life Benefits
$ in millions	2018			2017			2018			2017			2018			2017			2018			2017
Components of net periodic benefit cost
Service cost	$	100		$	97		$	5		$	6		$	199		$	194		$	10		$	11
Interest cost	300			312			19			21			590			625			38			42
Expected return on plan assets	(544		)	(472		)	(24		)	(23		)	(1,073		)	(943		)	(49		)	(45		)
Amortization of:
Prior service credit	(14		)	(14		)	(6		)	(6		)	(29		)	(29		)	(11		)	(11		)
Net loss from previous years	133			191			—			4			267			382			—			7
Net periodic benefit cost	$	(25	)	$	114		$	(6	)	$	2		$	(46	)	$	229		$	(12	)	$	4

Employer contributions to retirement plans

Contributions made by the company to its retirement plans are as follows:

	Three Months Ended June 30				Six Months Ended June 30
$ in millions	2018		2017		2018		2017
Defined benefit pension plans	$	23	$	28	$	45	$	51
Medical and life benefit plans	11		13		22		24
Defined contribution plans	88		77		192		176