Equity (Call Option Contracts) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended		3 Months Ended		6 Months Ended	0 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	0 Months Ended	3 Months Ended		6 Months Ended	0 Months Ended	1 Months Ended	2 Months Ended	3 Months Ended		6 Months Ended	3 Months Ended			3 Months Ended
	Dec. 31, 2012	Jun. 19, 2013	Mar. 31, 2013 Sold Call Options [Member] Series A Common Stock [Member]	Mar. 31, 2012 Sold Call Options [Member] Series A Common Stock [Member]	Dec. 31, 2013 Sold Call Options [Member] Series A Common Stock [Member]	Jun. 20, 2013 Sold Call Options [Member] Class A and Class C Ordinary Shares [Member]	Mar. 31, 2013 Sold Call Options [Member] Minimum [Member] Series A Common Stock [Member]	Dec. 31, 2013 Sold Call Options [Member] Minimum [Member] Series A Common Stock [Member]	Mar. 31, 2013 Sold Call Options [Member] Maximum [Member] Series A Common Stock [Member]	Dec. 31, 2013 Sold Call Options [Member] Maximum [Member] Series A Common Stock [Member]	Jun. 20, 2013 Purchased Call Option [Member] Series A Common Stock [Member]	Mar. 31, 2013 Purchased Call Option [Member] Series A Common Stock [Member]	Mar. 31, 2012 Purchased Call Option [Member] Series A Common Stock [Member]	Dec. 31, 2013 Purchased Call Option [Member] Series A Common Stock [Member]	Jun. 20, 2013 Call Option [Member]	Jan. 31, 2013 Call Option [Member]	Feb. 28, 2013 Call Option [Member]	Mar. 31, 2013 Call Option [Member]	Mar. 31, 2012 Call Option [Member]	Dec. 31, 2013 Call Option [Member]	Mar. 31, 2013 Call Option [Member] Series A Common Stock [Member]	Mar. 31, 2012 Call Option [Member] Series A Common Stock [Member]	Dec. 31, 2013 Call Option [Member] Class A Ordinary Shares [Member]	Mar. 31, 2012 Call Option [Member] Minimum [Member]	Mar. 31, 2012 Call Option [Member] Maximum [Member]
Call options (in shares)			1,000,000	3,520,000	3,726,759	1,512,000							0								400,000	1,000,000
Call options, exercise price (in dollars per share)						$ 100.00	$ 64.56	$ 69.66	$ 70.33	$ 81.71	$ 0	$ 0		$ 0										$ 54.73	$ 63.72
Aggregage call price paid for option contracts	$ (53.2)														$ 106.9	$ 12.3		$ 66.3	$ 204.9	$ 278.0
Proceeds from call options																	55.6	40.3	91.4
Distributable reserves, derivative asset		102.2
Distributable reserves, losses realized		4.7
Settlement in cash																				$ 196.7
Settlement in shares																							1,107,597