Quarterly Financial Data (unaudited) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	Oct. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Total revenue		$ 3,599	$ 3,518	$ 3,488	$ 3,411	$ 3,252	$ 3,161	$ 2,990	$ 2,748	$ 14,016	$ 12,151	$ 8,983
Income from continuing operations before income taxes		416	498	536	443	450	186	270	179	1,893	1,196	762
Income (loss) from discontinued operations, net of tax						(255)	16	(208)	23	0	(424)	97
Net income		318	441	442	369	195	202	62	202	1,570	661	754
Net income attributable to common shareholder		$ 296	$ 426	$ 427	$ 355	181	200	62	$ 202	$ 1,504	$ 645	$ 754
European Operations [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale of discontinued operations before income taxes	$ 525					$ 151	$ 38	$ 336