Capital and Other Regulatory Requirements Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Cash and Securities Segregated under Commodity Exchange Act Regulation	$ 1,574.7
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	1,550.6
Secured Funds	74.1
Secured Funds Required Under Commodity Exchange Act	62.5
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	98.7
Required Net Capital under Commodity Exchange Act	68.6
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	43.0
Required Net Capital under Commodity Exchange Act	21.4
Net Capital	90.6
Cash and Securities Segregated under Commodity Exchange Act Regulation	88.5
INTL Global Currencies [Member]
Net Capital under Commodity Exchange Act Computation	19.4
Required Net Capital under Commodity Exchange Act	0.5
TRX Futures [Member]
Net Capital	8.2
Capital Required for Capital Adequacy	3.0
INTL FCStone Securities [Member]
Net Capital	2.0
Minimum Net Capital Required for Entity	1.0
FCC Investments [Member]
Net Capital	0.4
Minimum Net Capital Required for Entity	0.3
FCStone Australia [Member]
Net Capital under Commodity Exchange Act Computation	2.0
Required Net Capital under Commodity Exchange Act	1.0
Net Capital	11.5
Capital Required for Capital Adequacy	0.8
FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	2.0
Required Net Capital under Commodity Exchange Act	0.5
INTL FCStone DTVM Ltda [Member]
Net Capital	0
Capital Required for Capital Adequacy	$ 0