Investments (Narrative) (Details) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) item	Jun. 30, 2019 USD ($) security item	Dec. 31, 2018 USD ($) security item
Investment [Line Items]
Increase (decrease) in gross AFS securities unrealized losses	$ (2,000)
Number of partnerships in alternative investment portfolio | item	248	248	237
Alternative investments as a percentage of overall invested assets		1.00%	1.00%
Fair value of collateral received that we are permitted to sell or re-pledge	$ 558	$ 558
Securities that have been re-pledged	450	450
Investment commitments	2,200	2,200
Investment commitments for limited partnerships	969	969
Investment commitments for mortgage loans on real estate	739	739
Investment commitments for private placements	521	$ 521
Commercial [Member]
Investment [Line Items]
Number of impaired loans | security		0	0
Residential [Member]
Investment [Line Items]
Number of impaired loans | security		0	0
Impaired financing receivable, allowance	2	$ 2
Maximum [Member] | Residential [Member]
Investment [Line Items]
Impaired financing receivable, allowance			$ 1
Federal Home Loan Mortgage Corporation [Member] | Invested Assets [Member]
Investment [Line Items]
Fair value	1,300	$ 1,300	$ 1,400
Concentration risk, percentage		1.00%	1.00%
Federal National Mortgage Association [Member] | Invested Assets [Member]
Investment [Line Items]
Fair value	1,300	$ 1,300	$ 1,300
Concentration risk, percentage		1.00%	1.00%
Consumer Non-Cyclical Industry [Member] | Invested Assets [Member]
Investment [Line Items]
Fair value	15,500	$ 15,500	$ 14,500
Concentration risk, percentage		12.00%	13.00%
Financial Service [Member] | Invested Assets [Member]
Investment [Line Items]
Fair value	$ 15,700	$ 15,700	$ 14,200
Concentration risk, percentage		12.00%	12.00%
Mortgage Loans On Real Estate [Member] | Geographic Concentration Risk [Member] | California [Member] | Commercial [Member]
Investment [Line Items]
Concentration risk, percentage		23.00%	23.00%
Mortgage Loans On Real Estate [Member] | Geographic Concentration Risk [Member] | California [Member] | Residential [Member]
Investment [Line Items]
Concentration risk, percentage		32.00%	34.00%
Mortgage Loans On Real Estate [Member] | Geographic Concentration Risk [Member] | Texas [Member] | Commercial [Member]
Investment [Line Items]
Concentration risk, percentage		12.00%	12.00%
Mortgage Loans On Real Estate [Member] | Geographic Concentration Risk [Member] | Florida [Member] | Residential [Member]
Investment [Line Items]
Concentration risk, percentage		20.00%	19.00%
Corporate Bonds [Member]
Investment [Line Items]
Percentage of fair value rated as investment grade	96.00%	96.00%	96.00%
Amortized cost of portfolio rated below investment grade	$ 3,200	$ 3,200	$ 3,200
Fair value of portfolio rated below investment grade	$ 3,200	$ 3,200	$ 3,000
MBS [Member]
Investment [Line Items]
Severity of second lien loans	100.00%	100.00%	100.00%
Severity of first lien loans	30.00%	30.00%	30.00%