Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2021

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)	2021		2020
Pension benefits
Service cost	$	26	$	28
Interest cost	46		56
Expected return on plan assets	(117)		(104)
Amortization of prior service credit	(13)		(14)
Costs and expenses	(58)		(34)
Remeasurement of projected benefit obligation	(512)		(116)
Remeasurement of plan assets	221		434
Remeasurement (gains) losses	(291)		318
Pension net (benefit) cost	$	(349)	$	284
Postretirement benefits
Service cost	$	—	$	1
Interest cost	2		3
Amortization of prior service credit	(6)		(1)
Costs and expenses	(4)		3
Remeasurement of projected benefit obligation	(19)		—
Remeasurement of plan assets	—		—
Remeasurement (gains) losses	(19)		—
Postretirement net (benefit) cost	$	(23)	$	3
Pension and postretirement benefits
Costs and expenses	$	(62)	$	(31)
Remeasurement (gains) losses	(310)		318
Total net (benefit) cost	$	(372)	$	287

Differences between expected and actual returns on plan assets and changes in assumptions affect the Company’s pension and other postretirement obligations, plan assets and expenses.

Pension and other postretirement service cost, interest cost, expected return on plan assets and amortization of prior service credit are reported in property and casualty insurance claims and claims expense, operating costs and expenses, net investment income and (if applicable) restructuring and related charges on the Condensed Consolidated Statement of Operations.

Pension and postretirement benefits remeasurement gains and losses
	Three months ended March 31,
($ in millions)	2021		2020
Remeasurement of projected benefit obligation (gains) losses:
Discount rate	$	(417)	$	(36)
Other assumptions	(114)		(80)
Remeasurement of plan assets (gains) losses	221		434
Remeasurement (gains) losses	$	(310)	$	318