Other Comprehensive Income (Tables)

12 Months Ended

Dec. 31, 2017

Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]

Other comprehensive income (loss) on a pre-tax and after-tax basis

Components of other comprehensive income (loss) on a pre-tax and after-tax basis
	For the years ended December 31,
($ in millions)	2017									2016									2015
	Pre-tax			Tax			After-tax			Pre-tax			Tax			After-tax			Pre-tax			Tax			After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$	866		$	(304	)	$	562		$	486		$	(170	)	$	316		$	(1,896	)	$	663		$	(1,233	)
Less: reclassification adjustment of realized capital gains and losses	374			(131		)	243			(180		)	63			(117		)	112			(39		)	73
Unrealized net capital gains and losses	492			(173		)	319			666			(233		)	433			(2,008		)	702			(1,306		)
Unrealized foreign currency translation adjustments	72			(25		)	47			15			(5		)	10			(89		)	31			(58		)
Unrecognized pension and other postretirement benefit cost arising during the period	232			(79		)	153			(263		)	94			(169		)	(64		)	25			(39		)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(237		)	83			(154		)	(100		)	35			(65		)	(134		)	47			(87		)
Unrecognized pension and other postretirement benefit cost	469			(162		)	307			(163		)	59			(104		)	70			(22		)	48
Other comprehensive income (loss)	$	1,033		$	(360	)	$	673		$	518		$	(179	)	$	339		$	(2,027	)	$	711		$	(1,316	)