Investments (Assets Supporting Experience-Rated Contractholder Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		$ 20,646	$ 21,299
Assets supporting experience-rated contractholder liabilities, at fair value	[1]	21,597	21,254
Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		18,904	19,706
Assets supporting experience-rated contractholder liabilities, at fair value		19,530	19,579
Equity securities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		1,465	1,378
Assets supporting experience-rated contractholder liabilities, at fair value		1,790	1,460
Short-term investments and cash equivalents
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		277	215
Assets supporting experience-rated contractholder liabilities, at fair value		277	215
Corporate securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		13,143	13,258
Assets supporting experience-rated contractholder liabilities, at fair value		13,603	13,119
Commercial mortgage-backed securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		1,845	2,346
Assets supporting experience-rated contractholder liabilities, at fair value		1,896	2,324
Residential mortgage-backed securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		1,134	828
Assets supporting experience-rated contractholder liabilities, at fair value		1,158	811
Asset-backed securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		1,639	1,649
Assets supporting experience-rated contractholder liabilities, at fair value		1,662	1,665
Foreign government bonds | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		802	1,087
Assets supporting experience-rated contractholder liabilities, at fair value		814	1,083
U.S. government authorities and agencies and obligations of U.S. states | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost		341	538
Assets supporting experience-rated contractholder liabilities, at fair value		$ 397	$ 577
Public Securities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost percentage		77.00%	78.00%
Collateralized loan obligations
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at fair value		$ 1,060	$ 1,028
NAIC High or Highest Quality Rating | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost percentage		94.00%	93.00%

[1] See Note 4 for details of balances associated with variable interest entities.