Principles of Consolidation And Other Matters (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) discrete_charge	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jan. 01, 2018 USD ($)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 189,000,000			$ 189,000,000
Equity method investments lag period				3 months
Gain (loss) on investment income, net	(52,000,000)		$ (2,000,000)	$ (24,000,000)	$ 3,000,000
Equity method investment, other than temporary impairment				81,000,000
Gains on equity investments	25,000,000			43,000,000
Equity method income	$ 4,000,000			$ 14,000,000
Effective tax rate (as a percent)	27.50%		26.20%	25.20%	25.90%
Number of discrete charges | discrete_charge		2
Period for payable on undistributed earnings				8 years
Provisional income tax expense (benefit)				$ 240,000,000
Transition tax for accumulated foreign earnings, liability	$ 3,400,000,000			3,400,000,000
Provisional withholding and state income tax expense (benefit)	226,000,000			53,000,000
Change in tax rate, deferred tax asset, provisional income tax expense (benefit)				220,000,000
Decrease to income tax expense (benefit)				14,000,000
Increase to income tax expense (benefit)				3,000,000
Unrecognized tax benefits	72,000,000	$ 71,000,000		72,000,000
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	$ 9,000,000			$ 9,000,000
Retained Earnings
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ 14,000,000				$ 14,000,000