Policyholders' Liabilities (Future Policy Benefits) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Life insurance	$ 172,586	$ 161,406
Individual and group annuities and supplementary contracts	67,090	63,486
Other contract liabilities	14,849	13,173
Subtotal future policy benefits excluding unpaid claims and claim settlement expenses	254,525	238,065
Unpaid claims and claim settlement expenses	2,792	2,843
Total future policy benefits	$ 257,317	$ 240,908