Retirement Benefits (Unaudited) (Tables)

9 Months Ended

Sep. 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 September 30												Nine Months Ended September 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	$	102		$	97		$	5		$	5		$	301		$	291		$	15		$	16
Interest cost	316			312			20			21			906			937			58			63
Expected return on plan assets	(571		)	(471		)	(26		)	(22		)	(1,644		)	(1,414		)	(75		)	(67		)
Amortization of:
Prior service credit	(15		)	(14		)	(5		)	(4		)	(44		)	(43		)	(16		)	(15		)
Net loss from previous years	135			171			(2		)	2			402			553			(2		)	9
Net periodic benefit cost	$	(33	)	$	95		$	(8	)	$	2		$	(79	)	$	324		$	(20	)	$	6

Employer contributions to retirement plans

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

	Three Months Ended September 30				Nine Months Ended September 30
$ in millions	2018		2017		2018		2017
Defined benefit pension plans	$	273	$	20	$	318	$	71
Medical and life benefit plans	10		11		32		35
Defined contribution plans	104		91		296		267