Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2019

Retirement Benefits [Abstract]

Company's pension and postretirement benefit plans

Components of net cost (benefit) for pension and other postretirement plans
	Three months ended March 31,
($ in millions)	2019			2018
Pension benefits
Service cost	$	28		$	28
Interest cost	65			61
Expected return on plan assets	(93		)	(113		)
Amortization of prior service credit	(14		)	(14		)
Costs and expenses	(14		)	(38		)
Remeasurement of projected benefit obligation	387			(190		)
Remeasurement of plan assets	(391		)	212
Remeasurement gains and losses	(4		)	22
Total net benefit	$	(18	)	$	(16	)
Postretirement benefits
Service cost	$	2		$	2
Interest cost	4			4
Amortization of prior service credit	(1		)	(5		)
Costs and expenses	5			1
Remeasurement of projected benefit obligation	19			(8		)
Remeasurement of plan assets	—			—
Remeasurement gains and losses	19			(8		)
Total net cost (benefit)	$	24		$	(7	)