Principles of Consolidation And Other Matters (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 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	$ 196,000,000
Equity method investments lag period	3 months
Gain (loss) on investment income, net	$ 5,000,000	$ (1,000,000)
Gains on equity investments	3,000,000
Equity method income	2,000,000	$ 7,000,000
Operating lease, liability	1,881,000,000
Operating lease, right-of-use asset	$ 1,625,000,000			$ 0
Effective tax rate (as a percent)	23.00%	23.90%
Excess tax benefit related to share-based payments (percent)	3.20%	2.40%
Unrecognized tax benefits	$ 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
Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits	$ 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