Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)		Dec. 31, 2016	Dec. 31, 2015
Financial instruments owned:
Exchange traded equity securities		$ 89,000,000	$ 0
Total assets measured at fair value		14,332,000,000	13,972,000,000
Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value		252,000,000	282,000,000
Fiduciary Assets:
Fiduciary assets		90,000,000	48,000,000
Liabilities:
Total liabilities measured at fair value		241,000,000	309,000,000
Identical Assets (Level 1)
Financial instruments owned:
Exchange traded equity securities		89,000,000	0
Total assets measured at fair value		2,618,000,000	2,576,000,000
Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value		252,000,000	282,000,000
Fiduciary Assets:
Fiduciary assets		90,000,000	48,000,000
Liabilities:
Total liabilities measured at fair value		0	0
Observable Inputs (Level 2)
Financial instruments owned:
Exchange traded equity securities		0	0
Total assets measured at fair value		3,452,000,000	3,123,000,000
Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value		0	0
Fiduciary Assets:
Fiduciary assets		0	0
Liabilities:
Total liabilities measured at fair value		0	0
Unobservable Inputs (Level 3)
Financial instruments owned:
Exchange traded equity securities		0	0
Total assets measured at fair value		323,000,000	260,000,000
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value		0	0
Fiduciary Assets:
Fiduciary assets		0	0
Liabilities:
Total liabilities measured at fair value		241,000,000	309,000,000
Other Assets | Fair Value, Measurements, Recurring
Financial instruments owned:
Mutual funds	[1]	141,000,000	142,000,000
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Mutual funds	[1]	141,000,000	142,000,000
Other Assets | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Mutual funds		0	0
Other Assets | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Mutual funds		0	0
Cash and Cash Equivalents | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	[2]	22,000,000	140,000,000
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	[2]	22,000,000	140,000,000
Cash and Cash Equivalents | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds		0	0
Cash and Cash Equivalents | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds		0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	[3]	241,000,000	309,000,000
Accounts Payable and Accrued Liabilities and Other Liabilities | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability		0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability		0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	[3]	241,000,000	309,000,000
Money Market Funds | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		90,000,000	48,000,000
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		90,000,000	48,000,000
Money Market Funds | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		0	0
Money Market Funds | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		$ 0	$ 0

[1] Included in other assets in the consolidated balance sheets.

[2] Included in cash and cash equivalents in the consolidated balance sheets.

[3] ncluded in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets.