Investments (Summary of fixed maturity and equity securities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Cost or Amortized Cost	$ 38,398	$ 37,633
Gross Unrealized Gains	4,639	3,149
Gross Unrealized Losses	155	541
Estimated fair value	42,882	40,241
Corporate and other bonds [Member]
Cost or Amortized Cost	19,530	19,086
Gross Unrealized Gains	2,698	1,946
Gross Unrealized Losses	21	154
Estimated fair value	22,207	20,878
Unrealized OTTI Losses (Gains)
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	9,372	9,018
Gross Unrealized Gains	1,455	900
Gross Unrealized Losses	44	136
Estimated fair value	10,783	9,782
Unrealized OTTI Losses (Gains)
Residential mortgage-backed [Member]
Cost or Amortized Cost	5,745	5,786
Gross Unrealized Gains	246	172
Gross Unrealized Losses	71	183
Estimated fair value	5,920	5,775
Unrealized OTTI Losses (Gains)	(28)	99
Commercial mortgage-backed [Member]
Cost or Amortized Cost	1,692	1,365
Gross Unrealized Gains	147	48
Gross Unrealized Losses	17	59
Estimated fair value	1,822	1,354
Unrealized OTTI Losses (Gains)	(3)	(2)
Other asset-backed [Member]
Cost or Amortized Cost	929	946
Gross Unrealized Gains	23	13
Gross Unrealized Losses		4
Estimated fair value	952	955
Unrealized OTTI Losses (Gains)
Total asset-backed [Member]
Cost or Amortized Cost	8,366	8,097
Gross Unrealized Gains	416	233
Gross Unrealized Losses	88	246
Estimated fair value	8,694	8,084
Unrealized OTTI Losses (Gains)	(31)	97
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	172	479
Gross Unrealized Gains	11	14
Gross Unrealized Losses	1
Estimated fair value	182	493
Unrealized OTTI Losses (Gains)
Foreign government [Member]
Cost or Amortized Cost	588	608
Gross Unrealized Gains	25	28
Gross Unrealized Losses
Estimated fair value	613	636
Unrealized OTTI Losses (Gains)
Redeemable preferred stock [Member]
Cost or Amortized Cost	113	51
Gross Unrealized Gains	13	7
Gross Unrealized Losses	1
Estimated fair value	125	58
Unrealized OTTI Losses (Gains)
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	38,141	37,339
Gross Unrealized Gains	4,618	3,128
Gross Unrealized Losses	155	536
Estimated fair value	42,604	39,931
Unrealized OTTI Losses (Gains)	(31)	97
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	29	6
Gross Unrealized Gains, Trading Securities
Gross Unrealized Losses, Trading Securities
Estimated Fair Value, Trading Securities	29	6
Common stock [Member]
Cost or Amortized Cost	38	30
Gross Unrealized Gains	14	17
Gross Unrealized Losses
Estimated fair value	52	47
Preferred stock [Member]
Cost or Amortized Cost	190	258
Gross Unrealized Gains	7	4
Gross Unrealized Losses		5
Estimated fair value	197	257
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	228	288
Gross Unrealized Gains	21	21
Gross Unrealized Losses		5
Estimated fair value	$ 249	$ 304

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

+ References+ Details