Retirement Benefits (Unaudited) (Tables)

9 Months Ended

Sep. 30, 2016

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	2016			2015			2016			2015			2016			2015			2016			2015
Components of net periodic benefit cost
Service cost	$	112		$	121		$	8		$	8		$	335		$	363		$	23		$	26
Interest cost	321			306			24			24			963			918			71			71
Expected return on plan assets	(464		)	(494		)	(21		)	(22		)	(1,390		)	(1,481		)	(64		)	(67		)
Amortization of:
Prior service credit	(15		)	(15		)	(6		)	(7		)	(45		)	(45		)	(17		)	(21		)
Net loss from previous years	179			170			3			6			536			511			11			20
Net periodic benefit cost	$	133		$	88		$	8		$	9		$	399		$	266		$	24		$	29

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	2016		2015		2016		2015
Defined benefit pension plans	$	14	$	20	$	61	$	564
Medical and life benefit plans	17		19		46		44
Defined contribution plans	83		77		241		227