Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 19,166		$ 46,798
Less than 12 months Gross Unrealized Losses	455		2,257
Twelve months or more Fair Value	19,666		17,981
Twelve months or more Gross Unrealized Losses	901		2,194
Total Fair Value	38,832	[1]	64,779	[2],[3]
Total Gross Unrealized Losses	1,356	[1]	4,451	[2],[3]
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	2,145		3,913
Less than 12 months Gross Unrealized Losses	5		95
Twelve months or more Fair Value	10		6
Twelve months or more Gross Unrealized Losses	0		1
Total Fair Value	2,155		3,919
Total Gross Unrealized Losses	5		96
Obligations of U.S. states and their political subdivisions [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	105		1,187
Less than 12 months Gross Unrealized Losses	1		129
Twelve months or more Fair Value	89		43
Twelve months or more Gross Unrealized Losses	2		8
Total Fair Value	194		1,230
Total Gross Unrealized Losses	3		137
Foreign Government Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	839		3,260
Less than 12 months Gross Unrealized Losses	26		211
Twelve months or more Fair Value	1,052		438
Twelve months or more Gross Unrealized Losses	91		55
Total Fair Value	1,891		3,698
Total Gross Unrealized Losses	117		266
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	11,326		29,574
Less than 12 months Gross Unrealized Losses	401		1,618
Twelve months or more Fair Value	13,346		14,094
Twelve months or more Gross Unrealized Losses	654		1,814
Total Fair Value	24,672		43,668
Total Gross Unrealized Losses	1,055		3,432
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	1,299		4,267
Less than 12 months Gross Unrealized Losses	6		128
Twelve months or more Fair Value	1,746		605
Twelve months or more Gross Unrealized Losses	33		35
Total Fair Value	3,045		4,872
Total Gross Unrealized Losses	39		163
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	3,417		2,995
Less than 12 months Gross Unrealized Losses	16		42
Twelve months or more Fair Value	3,229		2,511
Twelve months or more Gross Unrealized Losses	118		273
Total Fair Value	6,646		5,506
Total Gross Unrealized Losses	134		315
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	35		1,602
Less than 12 months Gross Unrealized Losses	0		34
Twelve months or more Fair Value	194		284
Twelve months or more Gross Unrealized Losses	3		8
Total Fair Value	229		1,886
Total Gross Unrealized Losses	3		42
Held-to-maturity Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Total Fair Value	91		210
Total Gross Unrealized Losses	$ 1		$ 24

[1] Includes $91 million of fair value and $1 million of gross unrealized losses at December 31, 2014, on securities classified as held-to-maturity, a portion of which is not reflected in AOCI.

[2] Includes $210 million of fair value and $24 million of gross unrealized losses at December 31, 2013, on securities classified as held-to-maturity, a portion of which is not reflected in AOCI. Prior period’s amounts are presented on a basis consistent with the current period presentation.

[3] Prior period’s amounts are presented on a basis consistent with the current period presentation.