Stock Plans (Tables)

12 Months Ended

Dec. 31, 2017

Stock Plans [Abstract]

LTIP Target Performance Shares

	Number of
	Shares
	(in thousands)
Balance at December 31, 2014	179
LTIP target performance shares granted	49
LTIP target performance shares earned	(50)
LTIP target performance shares forfeited	(10)
Balance at December 31, 2015	168
LTIP target performance shares granted	111
LTIP target performance shares earned	(59)
LTIP target performance shares forfeited	(30)
Balance at December 31, 2016	190
LTIP target performance shares granted	211
LTIP target performance shares earned	(41)
LTIP target performance shares forfeited	(54)
Balance at December 31, 2017	306

Restricted Shares Outstanding

		Weighted
		Average
	Number of	Grant Date		Aggregate
	Shares	Fair Value		Fair Value
	(in thousands)	(per share)		(in millions)
Balance at December 31, 2014	512	$	71.25	$	52
Restricted stock granted	188	$	118.80	$	13
Restricted stock vested	(214)	$	73.35	$	15
Restricted stock forfeited	(24)	$	76.50
Balance at December 31, 2015	462	$	88.95	$	33
Restricted stock granted	396	$	65.40	$	20
Restricted stock vested	(248)	$	78.90	$	13
Restricted stock forfeited	(61)	$	76.65
Balance at December 31, 2016	549	$	78.00	$	28
Restricted stock granted	454	$	47.77	$	3
Restricted stock vested	(240)	$	80.86	$	2
Restricted stock forfeited	(130)	$	60.92
Balance at December 31, 2017	633	$	58.63	$	4