Retirement Plans (Tables)

6 Months Ended

Jun. 30, 2018

Retirement Plans [Abstract]

Net Periodic Benefit Cost

	Pension Benefits
	For the three months ended				For the six months ended
	June 30,				June 30,
($ in millions)	2018		2017		2018		2017
Components of total pension benefit cost
Service cost	$	24	$	25	$	48	$	50
Interest cost on projected benefit obligation		30		33		60		67
Expected return on plan assets		(48)		(48)		(98)		(96)
Amortization of unrecognized loss		6		9		13		17
Net periodic pension benefit cost	$	12	$	19	$	23	$	38
Pension settlement costs		25		19		25		62
Total pension benefit cost	$	37	$	38	$	48	$	100
	Postretirement Benefits
	For the three months ended				For the six months ended
	June 30,				June 30,
($ in millions)	2018		2017		2018		2017
Components of net periodic postretirement benefit cost
Service cost	$	6	$	6	$	11	$	11
Interest cost on projected benefit obligation		10		9		19		19
Amortization of prior service cost/(credit)		(3)		(3)		(5)		(5)
Amortization of unrecognized (gain) loss		-		1		1		1
Net periodic postretirement benefit cost	$	13	$	13	$	26	$	26