Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Financial instruments owned:
Total assets measured at fair value		$ 14,378	$ 16,176
Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value		410	382
Fiduciary Assets:
Fiduciary assets		100	111
Liabilities:
Total liabilities measured at fair value		624	189
Identical Assets (Level 1)
Financial instruments owned:
Total assets measured at fair value		2,970	2,586
Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value		402	382
Fiduciary Assets:
Fiduciary assets		100	111
Liabilities:
Total liabilities measured at fair value		0	0
Observable Inputs (Level 2)
Financial instruments owned:
Total assets measured at fair value		4,261	4,238
Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value		8	0
Fiduciary Assets:
Fiduciary assets		0	0
Liabilities:
Total liabilities measured at fair value		116	0
Unobservable Inputs (Level 3)
Financial instruments owned:
Total assets measured at fair value		334	372
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		508	189
Other Assets | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	[1]	133	81
Mutual funds	[1]	151	158
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	[1]	133	81
Mutual funds	[1]	151	158
Other Assets | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	[1]	0	0
Mutual funds	[1]	0	0
Other Assets | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	[1]	0	0
Mutual funds	[1]	0	0
Cash and Cash Equivalents | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	[2]	118	143
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	[2]	118	143
Cash and Cash Equivalents | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	[2]	0	0
Cash and Cash Equivalents | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	[2]	0	0
Other Receivables | Fair Value, Measurements, Recurring
Financial instruments owned:
Other equity investment	[1]	8	0
Other Receivables | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Other equity investment	[1]	0	0
Other Receivables | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Other equity investment	[1]	8	0
Other Receivables | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Other equity investment	[1]	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	[3]	183	189
Accounts Payable and Accrued Liabilities and Other Liabilities | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	[3]	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	[3]	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	[3]	183	189
Money Market Funds | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		80	111
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		80	111
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
US Treasury Bills | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		20	0
US Treasury Bills | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		20	0
US Treasury Bills | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		0	0
US Treasury Bills | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets		0	0
Senior Debt Obligations Due 2014 | Long-term Debt | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contract		441	0
Senior Debt Obligations Due 2014 | Long-term Debt | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contract		0	0
Senior Debt Obligations Due 2014 | Long-term Debt | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contract		116	0
Senior Debt Obligations Due 2014 | Long-term Debt | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contract		$ 325	$ 0

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

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

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