Schedule II - Condensed Financial Information, Credit Facility (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Banks
Line of Credit Facility [Line Items]
Debt outstanding	$ 5,200
Debt Instrument, Covenant Compliance	The Company was in compliance with its debt covenants as of December 31, 2015. The Company was in compliance with its debt covenants as of December 31, 2015.
Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit agreement term	5 years
Maximum borrowing capacity under credit facility	$ 1,500
Number of participating banks | Banks	16
Total commitment amount under option to increase borrowing capacity	$ 2,000
Expiration date	Dec. 31, 2019
Covenant terms	This agreement has certain covenants, including a financial covenant requiring the Company to maintain a leverage ratio of total consolidated debt-to-consolidated capitalization (each defined in the credit agreement) at or below 0.50.
Leverage ratio covenant	50.00%
Additional borrowing capacity under maximum debt coverage covenant	$ 7,900
Line of Credit Facility, Covenant Compliance	The Company was in compliance with its debt covenants as of December 31, 2015.
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility	$ 500
Letters of credit outstanding	$ 19
Primary Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Number of participating banks | Banks	3
Percent held by each primary commitment holder	12.00%
Minor Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Number of participating banks | Banks	13
Collective percentage held by secondary commitment holders	64.00%
Parent Company [Member]
Line of Credit Facility [Line Items]
Debt outstanding	$ 5,000
Debt Instrument, Covenant Compliance	The Company was in compliance with its debt covenants as of December 31, 2015
Parent Company [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit agreement term	5 years
Maximum borrowing capacity under credit facility	$ 1,500
Number of participating banks	16
Total commitment amount under option to increase borrowing capacity	$ 2,000
Expiration date	Dec. 31, 2019
Covenant terms	The credit agreement contains customary covenants and restrictions, including a financial covenant that the Company may not permit its leverage ratio to be greater than 0.50. The leverage ratio is total consolidated debt to total consolidated capitalization (each as defined in the credit agreement) and excludes net unrealized appreciation in fixed maturities and the portion of the post-retirement benefits liability adjustment attributable to pension that is included in accumulated other comprehensive loss on the Company’s consolidated balance sheet.
Leverage ratio covenant	50.00%
Additional borrowing capacity under maximum debt coverage covenant	$ 7,900
Line of Credit Facility, Covenant Compliance	The Company was in compliance with its debt covenants as of December 31, 2015
Parent Company [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility	$ 500
Letters of credit outstanding	$ 19
Parent Company [Member] | Primary Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Number of participating banks	3
Percent held by each primary commitment holder	12.00%
Parent Company [Member] | Minor Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Number of participating banks	13
Collective percentage held by secondary commitment holders	64.00%