Investments (Unconsolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Carrying Amount Asset	$ 54,803	$ 56,381
Carrying Amount Liability	59,202	60,429
Other limited partnership interests
Variable Interest Entity [Line Items]
Carrying Amount Asset	5,088	4,834
Carrying Amount Liability	9,269	8,543
Other invested assets
Variable Interest Entity [Line Items]
Carrying Amount Asset	1,866	2,291
Carrying Amount Liability	2,080	2,625
Other
Variable Interest Entity [Line Items]
Carrying Amount Asset	37	82
Carrying Amount Liability	41	87
Structured securities (RMBS, CMBS, and ABS)
Variable Interest Entity [Line Items]
Carrying Amount Asset	46,531	47,614
Carrying Amount Liability	46,531	47,614
U.S. corporate and foreign corporate securities
Variable Interest Entity [Line Items]
Carrying Amount Asset	1,281	1,560
Carrying Amount Liability	$ 1,281	$ 1,560