Debt worldwide has increased more than 40 percent since 2007, according to Bank for International Settlements.

Agency is said to be exploring whether foreign exchange rate rigging distorted options prices.

Morgan Stanley and Goldman Sachs are said to have gotten credit as advisers on an M&A deal they didn't work on, by lowering fees they were owed.

Junk-rated deals continue to leave companies with debt levels that exceed regulator guidelines.