Fair Value Of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Of Financial Instruments [Abstract]

Fair Value Of Long-Term Debt

	March 31, 2018				December 31, 2017
($ in millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt	$	16,470	$	13,522	$	16,970	$	13,994