Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2014

Quarterly Financial Information Disclosure [Abstract]

Quarterly financial data

	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	(millions, except per share data)
2014
Total revenues	$	1,097		$	935		$	812		$	958
Total expenses	(771		)	(787		)	(778		)	(819		)
Net income (loss)	250			48			(8		)	83
Net income (loss) attributable to Willis Group Holdings	246			47			(7		)	76
Earnings per share
— Basic	$	1.37		$	0.26		$	(0.04	)	$	0.43
— Diluted	$	1.35		$	0.26		$	(0.04	)	$	0.42
2013
Total revenues	$	1,051		$	890		$	795		$	919
Total expenses	(770		)	(723		)	(725		)	(774		)
Net income (loss)	223			107			(27		)	74
Net income (loss) attributable to Willis Group Holdings	219			105			(27		)	68
Earnings per share
— Basic	$	1.27		$	0.60		$	(0.15	)	$	0.38
— Diluted	$	1.24		$	0.59		$	(0.15	)	$	0.37