Fair Value Measurements (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended |
Sep. 30, 2018 | Dec. 31, 2017 |
Asset of BSIF and consolidated Funds | | |
Other investments | $ 0 | $ 6.4 |
Investments at fair value | 344 | 319.3 |
Liabilities of consolidated Funds | | |
Investment carried at cost | | 60.2 |
Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Investments at fair value | 135.4 | 136.7 |
Consolidated Entity Excluding Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Total fair value assets | 208.6 | 182.6 |
Recurring | | |
Asset of BSIF and consolidated Funds | | |
Total fair value assets | 344 | 319.3 |
Liabilities of consolidated Funds | | |
Total fair value liabilities | (1.4) | (7.9) |
Recurring | Investment funds | | |
Asset of BSIF and consolidated Funds | | |
Alternative investments, fair value disclosure | $ 58.6 | 92.8 |
Recurring | Investment funds | Minimum | | |
Liabilities of consolidated Funds | | |
Term over which the underlying assets are expected to be liquidated by the investees | 1 year | |
Recurring | Investment funds | Maximum | | |
Liabilities of consolidated Funds | | |
Term over which the underlying assets are expected to be liquidated by the investees | 12 years | |
Recurring | Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Common and preferred stock | $ 45.7 | 83.8 |
Short-term investment funds | 25.7 | 0.5 |
Bank loans | 58.8 | |
Other investments | 4.4 | 51.9 |
Derivatives | 0.8 | 0.5 |
Total fair value assets | 135.4 | 136.7 |
Liabilities of consolidated Funds | | |
Common stock | (0.9) | (7.2) |
Derivatives | (0.5) | (0.7) |
Total fair value liabilities | (1.4) | (7.9) |
Recurring | Consolidated Funds | Other Investments | | |
Asset of BSIF and consolidated Funds | | |
Alternative investments, fair value disclosure | 0 | 51.5 |
Recurring | Consolidated Entity Excluding Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Investments in separate accounts | 43.3 | 46.1 |
Investments related to long-term incentive compensation plans | 102.1 | 95.2 |
Alternative investments, fair value disclosure | 58.6 | |
Total fair value assets | 208.6 | 182.6 |
Recurring | Consolidated Entity Excluding Consolidated Funds | Investment funds | | |
Asset of BSIF and consolidated Funds | | |
Alternative investments, fair value disclosure | 58.6 | 41.3 |
Investments at fair value | 63.2 | 41.3 |
Recurring | Quoted prices in active markets (Level I) | | |
Asset of BSIF and consolidated Funds | | |
Total fair value assets | 215.2 | 226.3 |
Liabilities of consolidated Funds | | |
Total fair value liabilities | (1.3) | (7.7) |
Recurring | Quoted prices in active markets (Level I) | Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Common and preferred stock | 45.7 | 83.8 |
Short-term investment funds | 25.7 | 0.5 |
Bank loans | 0 | |
Other investments | 0 | 0.4 |
Derivatives | 0.7 | 0.3 |
Total fair value assets | 72.1 | 85 |
Liabilities of consolidated Funds | | |
Common stock | (0.9) | (7.2) |
Derivatives | (0.4) | (0.5) |
Total fair value liabilities | (1.3) | (7.7) |
Recurring | Quoted prices in active markets (Level I) | Consolidated Entity Excluding Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Investments in separate accounts | 41 | 46.1 |
Investments related to long-term incentive compensation plans | 102.1 | 95.2 |
Total fair value assets | $ 143.1 | $ 141.3 |
Liabilities of consolidated Funds | | |
Investment in cash | 4.00% | 1.00% |
Investment in equity securities | 96.00% | 99.00% |
Recurring | Quoted prices in active markets (Level I) | Consolidated Entity Excluding Consolidated Funds | Investment funds | | |
Asset of BSIF and consolidated Funds | | |
Investments at fair value | $ 0 | $ 0 |
Recurring | Significant other observable inputs (Level II) | | |
Asset of BSIF and consolidated Funds | | |
Total fair value assets | 65.6 | 0.2 |
Liabilities of consolidated Funds | | |
Total fair value liabilities | (0.1) | (0.2) |
Recurring | Significant other observable inputs (Level II) | Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Common and preferred stock | 0 | 0 |
Short-term investment funds | 0 | 0 |
Bank loans | 58.8 | |
Other investments | 4.4 | 0 |
Derivatives | 0.1 | 0.2 |
Total fair value assets | 63.3 | 0.2 |
Liabilities of consolidated Funds | | |
Common stock | 0 | 0 |
Derivatives | (0.1) | (0.2) |
Total fair value liabilities | (0.1) | (0.2) |
Recurring | Significant other observable inputs (Level II) | Consolidated Entity Excluding Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Investments in separate accounts | 2.3 | 0 |
Investments related to long-term incentive compensation plans | 0 | 0 |
Total fair value assets | 2.3 | 0 |
Recurring | Significant other observable inputs (Level II) | Consolidated Entity Excluding Consolidated Funds | Investment funds | | |
Asset of BSIF and consolidated Funds | | |
Investments at fair value | 0 | 0 |
Recurring | Significant unobservable inputs (Level III) | | |
Asset of BSIF and consolidated Funds | | |
Total fair value assets | 4.6 | 0 |
Liabilities of consolidated Funds | | |
Total fair value liabilities | 0 | 0 |
Recurring | Significant unobservable inputs (Level III) | Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Common and preferred stock | 0 | 0 |
Short-term investment funds | 0 | 0 |
Bank loans | 0 | |
Other investments | 0 | 0 |
Derivatives | 0 | 0 |
Total fair value assets | 0 | 0 |
Liabilities of consolidated Funds | | |
Common stock | 0 | 0 |
Derivatives | 0 | 0 |
Total fair value liabilities | 0 | 0 |
Recurring | Significant unobservable inputs (Level III) | Consolidated Entity Excluding Consolidated Funds | | |
Asset of BSIF and consolidated Funds | | |
Investments in separate accounts | 0 | 0 |
Investments related to long-term incentive compensation plans | 0 | 0 |
Total fair value assets | 4.6 | 0 |
Recurring | Significant unobservable inputs (Level III) | Consolidated Entity Excluding Consolidated Funds | Investment funds | | |
Asset of BSIF and consolidated Funds | | |
Investments at fair value | 4.6 | $ 0 |
Heitman LLC | Affiliates | | |
Liabilities of consolidated Funds | | |
Gain on sale of investment | $ 65.7 | |