Complex sentence: Arthur Andersen LLP, based in Chicago, is an American holding company and formerly one of the "Big Five" accounting firms among PricewaterhouseCoopers, Deloitte Touche Tohmatsu, Ernst & Young and KPMG, providing auditing, tax, and consulting services to large corporations.
Split into simpler sentences: Arthur Andersen LLP, based in Chicago, is an American holding company. Formerly one of the "Big Five" accounting firms (almong with PricewaterhouseCoopers, Deloitte Touche Tohmatsu, Ernst & Young, and KPMG), the firm had provided auditing, tax, and consulting services to large corporations.