Employee Stock and Incentive Plans - Performance Shares and Restricted Stock Units (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Performance Shares [Member]
Number of Shares [Abstract]
As of January 1,	114,765	107,899	107,899		128,333		122,489
Granted	43,081	41,332	45,830	[1]	38,764	[1]	39,312	[1]
Awarded	(36,515)	(18,605)	(18,605)		(41,009)		(32,368)
Unearned Grant Award			(18,606)		(17,575)		0
Forfeited			(1,753)		(614)		(1,100)
As of December 31,			114,765		107,899		128,333
Weighted Average Grant Date Fair Value [Abstract]
As of January 1,	$ 47.02	$ 40.73	$ 40.73		$ 36.54		$ 38.15
Granted			$ 52.15	[1]	$ 44.70	[1]	$ 41.00	[1]
Awarded			$ 35.10		$ 34.25		$ 48.10
Unearned Grant Award			$ 35.10		$ 34.25		$ 0.00
Forfeited			$ 47.26		$ 34.49		$ 34.35
As of December 31,			$ 47.02		$ 40.73		$ 36.54
Performance Period			3 years
Grants, Grant Date Fair Value	$ 2.0	$ 2.2
Awards, Grant Date Fair Value	1.5	0.7
Restricted Stock Units [Member]
Number of Shares [Abstract]
As of January 1,	55,982	56,415	56,415		63,464		43,803
Granted	17,491	19,193	21,440	[1]	18,162	[1]	20,136	[1]
Awarded	(18,860)		(20,939)		(24,707)		(215)
Forfeited			(934)		(504)		(260)
As of December 31,			55,982		56,415		63,464
Weighted Average Grant Date Fair Value [Abstract]
As of January 1,	$ 40.85	$ 36.61	$ 36.61		$ 32.57		$ 30.61
Granted			$ 43.41	[1]	$ 40.83	[1]	$ 36.74	[1]
Awarded			$ 32.03		$ 29.43		$ 30.30
Forfeited			$ 41.02		$ 31.80		$ 29.41
As of December 31,			$ 40.85		$ 36.61		$ 32.57
Performance Period			3 years
Grants, Grant Date Fair Value	0.9	0.8
Awards, Grant Date Fair Value	$ 0.7		$ 0.7

[1] Shares granted includes accrued dividends.