The move by Volk was disclosed in an internal memo, Bloomberg reported. Volk joined the company as a vice chairman and is also chairman of the bank's institutional-clients group.
“Steve has helped bring in and maintain some of our most important and durable client relationships," Citi Chief Executive Michael Corbat wrote in the memo, according to Bloomberg.
Paco Ybarra is CEO of the institutional clients group, Bloomberg reported.
Volk joined Citi after serving as chairman at Credit Suisse First Boston. He'd also served as a senior partner at the New York law firm Shearman & Sterling.
Volk also is currently a member of the Council on Foreign Relations, the New York think tank focused on international affairs.
During his time as a lawyer, Volk oversaw DuPont's $7.6 billion purchase of a controlling stake in Conoco, which was the largest ever acquisition at the time.
He also helped shepherd the $8.3 billion merger between Paramount Communications and Viacom about a decade later.
In October, Citigroup said third-quarter earnings were $1.40 a share, down 32% from the year-earlier quarter but ahead of the Wall Street consensus forecast of 93 cents a share.
Group revenue, Citigroup reported, fell 6.8% to $17.3 billon, edging ahead of analysts' forecasts of a $17.2 billion tally.
Citi shares at last check rose 2.8% to $57.05.