(1985) ([R]ather than explicitly enumerating all of the powers and duties of trustees and other fiduciaries, Congress invoked the common law of trusts to define the general scope of their authority and responsibility); H. R. Rep. No. 93-533, pp. 3-5, 11-13 (1973), 2 Legislative History of the Employment Retirement Income Security Act of 1974 (Committee Print compiled for the Senate Subcommittee