Fair Value Accounting (Details) (Fair value measurements, recurring, USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Level 1
Assets:
Cash equivalents	$ 348.8		$ 230.6
Restricted cash	237.9		260.7
Total assets	586.7		491.3
Liabilities:
Total liabilities	0		0
Level 1 | Interest rate hedges | Wholly-owned subsidiaries
Liabilities:
Interest rate hedges	0	[1]	0	[1]
Level 1 | Interest rate hedges | Partially-owned subsidiaries
Liabilities:
Interest rate hedges	0	[1]	0	[1]
Level 2
Assets:
Cash equivalents	0		0
Restricted cash	0		0
Total assets	0		0
Liabilities:
Total liabilities	12.1		23.8
Level 2 | Interest rate hedges | Wholly-owned subsidiaries
Liabilities:
Interest rate hedges	10.3	[1]	21.7	[1]
Level 2 | Interest rate hedges | Partially-owned subsidiaries
Liabilities:
Interest rate hedges	1.8	[1]	2.1	[1]
Level 3
Assets:
Cash equivalents	0		0
Restricted cash	0		0
Total assets	0		0
Liabilities:
Total liabilities	0		0
Level 3 | Interest rate hedges | Wholly-owned subsidiaries
Liabilities:
Interest rate hedges	0	[1]	0	[1]
Level 3 | Interest rate hedges | Partially-owned subsidiaries
Liabilities:
Interest rate hedges	0	[1]	0	[1]
Total
Assets:
Cash equivalents	348.8		230.6
Restricted cash	237.9		260.7
Total assets	586.7		491.3
Liabilities:
Total liabilities	12.1		23.8
Total | Interest rate hedges | Wholly-owned subsidiaries
Liabilities:
Interest rate hedges	10.3	[1]	21.7	[1]
Total | Interest rate hedges | Partially-owned subsidiaries
Liabilities:
Interest rate hedges	$ 1.8	[1]	$ 2.1	[1]

[1] Included in accrued liabilities on the consolidated balance sheet.