Retirement Benefits (Unaudited) (Tables)

9 Months Ended

Sep. 30, 2017

Compensation and Retirement Disclosure [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	2017			2016			2017			2016			2017			2016			2017			2016
Components of net periodic benefit cost
Service cost	$	94		$	112		$	6		$	8		$	322		$	335		$	19		$	23
Interest cost	308			321			21			24			925			963			63			71
Expected return on plan assets	(471		)	(464		)	(22		)	(21		)	(1,414		)	(1,390		)	(67		)	(64		)
Amortization of:
Prior service credit	(14		)	(15		)	(4		)	(6		)	(43		)	(45		)	(15		)	(17		)
Net loss from previous years	178			179			1			3			534			536			6			11
Net periodic benefit cost	$	95		$	133		$	2		$	8		$	324		$	399		$	6		$	24

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	2017		2016		2017		2016
Defined benefit pension plans	$	20	$	14	$	71	$	61
Medical and life benefit plans	11		17		35		46
Defined contribution plans	91		83		267		241