Investments (Net Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 15,738	$ 15,994	$ 15,312
Less: investment expenses	(909)	(738)	(583)
Net investment income	14,829	15,256	14,729
Fixed maturities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	10,347	10,558	10,541
Fixed maturities, held-to-maturity
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	202	185	125
Equity securities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	337	354	337
Trading account assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	1,205	1,074	963
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	2,255	2,103	1,985
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	619	632	611
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	56	38	40
Other long-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 717	$ 1,050	$ 710