Cash Flow Information - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash Balance (Detail) - USD ($) $ in Millions	Mar. 30, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 1,017	$ 846	$ 1,026	$ 1,047
Cash and investments segregated under federal regulations	9,069	10,099	12,516	12,680
Less: Investments segregated under federal regulations	2,006	2,408	4,146	4,155
Total cash, cash equivalents and restricted cash	$ 8,080	$ 8,537	$ 9,396	$ 9,572