Principles of Consolidation And Other Matters (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 192,000,000		$ 192,000,000			$ 186,000,000
Equity method investments lag period			3 months
Gain (loss) on investment income, net	8,000,000	$ 28,000,000	$ 13,000,000	$ 28,000,000
Gains on equity investments	3,000,000	26,000,000	6,000,000	19,000,000
Equity method income	5,000,000	$ 2,000,000	7,000,000	$ 9,000,000
Operating lease, liability	2,328,000,000		2,328,000,000
Operating lease, right-of-use asset	$ 2,016,000,000		$ 2,016,000,000			0
Effective tax rate (as a percent)	37.40%	25.60%	28.20%	24.70%
Unrecognized tax benefits	$ 74,000,000		$ 74,000,000			$ 78,000,000
Minimum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits	0		0
Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits	$ 10,000,000		$ 10,000,000
Accounting Standards Update 2016-02
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating lease, liability					$ 1,900,000,000
Operating lease, right-of-use asset					1,700,000,000
Restatement Adjustment | Accounting Standards Update 2016-02
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Other liabilities					$ 200,000,000