Investments (Assets Supporting Experience-Rated Contractholder Liabilities) (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		$ 21,471	$ 20,646
Assets supporting experience-rated contractholder liabilities, at fair value	[1]	21,580	21,597
Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		18,903	18,904
Assets supporting experience-rated contractholder liabilities, at fair value		19,031	19,530
Equity securities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		1,485	1,465
Assets supporting experience-rated contractholder liabilities, at fair value		1,466	1,790
Short-term investments and cash equivalents
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		1,083	277
Assets supporting experience-rated contractholder liabilities, at fair value		1,083	277
Corporate securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		13,102	13,143
Assets supporting experience-rated contractholder liabilities, at fair value		13,110	13,603
Commercial mortgage-backed securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		1,828	1,845
Assets supporting experience-rated contractholder liabilities, at fair value		1,869	1,896
Residential mortgage-backed securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		1,208	1,134
Assets supporting experience-rated contractholder liabilities, at fair value		1,243	1,158
Asset-backed securities | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		1,637	1,639
Assets supporting experience-rated contractholder liabilities, at fair value		1,607	1,662
Foreign government bonds | Fixed maturities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost or cost		785	802
Assets supporting experience-rated contractholder liabilities, at fair value		791	814
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 or cost		343	341
Assets supporting experience-rated contractholder liabilities, at fair value		$ 411	$ 397
Public Securities
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at amortized cost percentage		78.00%	77.00%
Collateralized loan obligations
Assets Supporting Experience-Rated Contractholder Liabilities [Line Items]
Assets supporting experience-rated contractholder liabilities, at fair value		$ 1,009	$ 1,060
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%	94.00%

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