Segment Information - Financial Information for Partnership's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 28, 2025	Mar. 29, 2024	Dec. 31, 2024
Revenues From External Customers And Long Lived Assets [Line Items]
Net revenue	$ 4,167	$ 3,794
FA compensation	1,653	1,479
Home office operating expenses	805	743
Branch office operating expense	585	555
Variable compensation	611	550
Total operating expenses	3,654	3,327
Income before allocations	$ 513	$ 467
Income before allocations margin	12.20%	12.10%
Net interest and dividends revenue	$ 219	$ 240
Depreciation and amortization	164	143
Assets	27,980	27,737	$ 28,964
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Net revenue	4,047	3,688
FA compensation	1,605	1,437
Home office operating expenses	778	717
Branch office operating expense	568	538
Variable compensation	598	539
Total operating expenses	3,549	3,231
Income before allocations	$ 498	$ 457
Income before allocations margin	12.10%	12.20%
Net interest and dividends revenue	$ 206	$ 228
Depreciation and amortization	159	139
Assets	26,758	26,646
Canada [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Net revenue	120	106
FA compensation	48	42
Home office operating expenses	27	26
Branch office operating expense	17	17
Variable compensation	13	11
Total operating expenses	105	96
Income before allocations	$ 15	$ 10
Income before allocations margin	12.80%	9.30%
Net interest and dividends revenue	$ 13	$ 12
Depreciation and amortization	5	4
Assets	$ 1,222	$ 1,091