Supplementary Quarterly Financial Data (unaudited) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Total revenue	$ 3,636	$ 3,659	$ 3,639	$ 3,620	$ 3,599	$ 3,518	$ 3,488	$ 3,411	$ 14,554	$ 14,016	$ 12,151
Income from continuing operations before income taxes	498	711	536	359	416	498	536	443	2,104	1,893	1,196
Net income	377	516	403	271	318	441	442	369	1,567	1,570	661
Net income attributable to common shareholder	$ 355	$ 493	$ 381	$ 248	$ 296	$ 426	$ 427	$ 355	$ 1,477	$ 1,504	$ 645