Quarterly Results of Operations (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2018	[1]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Results of Operations [Abstract]
Total revenues	$ 4,063		$ 4,039	$ 3,852	$ 3,404	$ 3,413		$ 3,269	$ 3,237	$ 3,229	$ 15,358	$ 13,148	$ 12,343
Total expenses	3,631		3,619	3,357	2,921	3,887		2,809	2,840	2,881	13,528	12,417	10,903
Net income (loss)	$ 368		$ 378	$ 420	$ 407	$ 963		$ 385	$ 321	$ 349	$ 1,573	$ 2,018	$ 1,173

[1] Fourth quarter 2017 results include a goodwill impairment charge and the impacts of remeasuring our existing deferred tax balances for the impact of the Tax Act as disclosed elsewhere herein.