Summary of Significant Accounting Policies - Goodwill and Intangible Assets, Net (Details)		3 Months Ended								12 Months Ended
		Dec. 31, 2015 USD ($) $ / shares	Sep. 30, 2015 $ / shares	Jun. 30, 2015 $ / shares	Mar. 31, 2015 $ / shares	Dec. 31, 2014 USD ($) $ / shares	Sep. 30, 2014 $ / shares	Jun. 30, 2014 $ / shares	Mar. 31, 2014 $ / shares	Dec. 31, 2015 USD ($) segment reporting_unit	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2000 USD ($)
Business Acquisition [Line Items]
Cash distribution, distribution declared (in dollars per unit) | $ / shares	[1],[2]	$ 0.56	$ 0.50	$ 0.54	$ 0.51	$ 0.63	$ 0.51	$ 0.50	$ 0.44
Goodwill [Abstract]
Goodwill		$ 3,044,807,000				$ 3,044,807,000				$ 3,044,807,000	$ 3,044,807,000
Number of reportable segments | segment										1
Number of reporting units | reporting_unit										1
Intangible Assets, Net [Abstract]
Intangible assets, net of accumulated amortization		145,710,000				171,407,000				$ 145,710,000	171,407,000
Definite-lived intangible assets subject to amortization, net		132,200,000				157,900,000				132,200,000	157,900,000
Indefinite-lived intangible assets not subject to amortization		13,500,000				13,500,000				13,500,000	13,500,000
Gross carrying amount of intangible assets		460,800,000				460,700,000				460,800,000	460,700,000
Accumulated amortization of intangible assets		328,600,000				302,800,000				328,600,000	302,800,000
Amortization expense on intangible assets										25,798,000	24,916,000	$ 21,859,000
Future estimated annual amortization expense [Abstract]
2016		26,000,000								26,000,000
2017		26,000,000								26,000,000
2018		26,000,000								26,000,000
2019		26,000,000								26,000,000
2020		26,000,000								26,000,000
Total cash distributions per unit paid to unitholders (in dollars per unit)										$ 2.18	2.11	$ 1.69
Minimum [Member]
Intangible Assets, Net [Abstract]
Intangible assets acquired, estimated useful life										6 years
Maximum [Member]
Intangible Assets, Net [Abstract]
Intangible assets acquired, estimated useful life										20 years
Sanford C Bernstein Inc Acquisition [Member]
Goodwill [Abstract]
Goodwill acquired during period													$ 3,000,000,000
Goodwill		2,800,000,000								$ 2,800,000,000
Intangible Assets, Net [Abstract]
Definite-lived intangible assets subject to amortization, net		98,300,000				$ 119,000,000				98,300,000	$ 119,000,000
Series of Individually Immaterial Business Acquisitions [Member]
Goodwill [Abstract]
Goodwill		$ 244,000,000								$ 244,000,000

[1] Cash distributions reflect the impact of our non-GAAP adjustments.

[2] Declared and paid during the following quarter.