Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) (Hedge funds, USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Investment securities
Other long-term investments	$ 117.7
Distributions from inactive hedge funds	2.6
Redemption requests	7.1
Monthly
Investment securities
Other long-term investments	6.8
Quarterly
Investment securities
Other long-term investments	77.7
Semi-annual
Investment securities
Other long-term investments	22.7
Annual
Investment securities
Other long-term investments	10.5
30-59 days notice
Investment securities
Other long-term investments	29.6
30-59 days notice | Monthly
Investment securities
Other long-term investments	0
30-59 days notice | Quarterly
Investment securities
Other long-term investments	27.9
30-59 days notice | Semi-annual
Investment securities
Other long-term investments	0
30-59 days notice | Annual
Investment securities
Other long-term investments	1.7
60-89 days notice
Investment securities
Other long-term investments	53.9
60-89 days notice | Monthly
Investment securities
Other long-term investments	0
60-89 days notice | Quarterly
Investment securities
Other long-term investments	31.2
60-89 days notice | Semi-annual
Investment securities
Other long-term investments	22.7
60-89 days notice | Annual
Investment securities
Other long-term investments	0
90-119 days notice
Investment securities
Other long-term investments	17.5
90-119 days notice | Monthly
Investment securities
Other long-term investments	0
90-119 days notice | Quarterly
Investment securities
Other long-term investments	9.0
90-119 days notice | Semi-annual
Investment securities
Other long-term investments	0
90-119 days notice | Annual
Investment securities
Other long-term investments	8.5
120+ days notice
Investment securities
Other long-term investments	16.7
120+ days notice | Monthly
Investment securities
Other long-term investments	6.8
120+ days notice | Quarterly
Investment securities
Other long-term investments	9.6
120+ days notice | Semi-annual
Investment securities
Other long-term investments	0
120+ days notice | Annual
Investment securities
Other long-term investments	$ 0.3