Quarterly Financial Data (unaudited) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	Oct. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Total revenue		$ 3,252	$ 3,161	$ 2,990	$ 2,748	$ 2,554	$ 2,360	$ 2,138	$ 1,931	$ 12,151	$ 8,983	$ 5,867
Income from continuing operations		450	186	270	179	242	134	143	138	1,196	762	679
Income (loss) from discontinued operations, net of tax		(255)	16	(208)	23	12	13	46	26	(424)	97	161
Net income		195	202	62	$ 202	$ 254	$ 147	$ 189	$ 164	$ 661	$ 754	$ 646
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