Fair Value Measurements - Separate Account Assets (Details) (USD $) In Millions, unless otherwise specified					3 Months Ended				6 Months Ended
	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2013 Separate Accounts [Member]		Jun. 30, 2012 Separate Accounts [Member]		Jun. 30, 2013 Separate Accounts [Member]		Jun. 30, 2012 Separate Accounts [Member]		Jun. 30, 2013 Pension Benefits [Member]	Dec. 31, 2012 Pension Benefits [Member]	Jun. 30, 2013 Fair Value Inputs Level 1 [Member]	Dec. 31, 2012 Fair Value Inputs Level 1 [Member]	Jun. 30, 2013 Fair Value Inputs Level 2 [Member]	Dec. 31, 2012 Fair Value Inputs Level 2 [Member]	Jun. 30, 2013 Fair Value Inputs Level 3 [Member]	Dec. 31, 2012 Fair Value Inputs Level 3 [Member]	Jun. 30, 2013 Fair Value Inputs Level 3 [Member] Pension Benefits [Member]	Dec. 31, 2012 Fair Value Inputs Level 3 [Member] Pension Benefits [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts	$ 508		$ 569												$ 231	$ 245	$ 277	$ 324	$ 0	$ 0
Non-guaranteed separate accounts	7,457	[1]	7,188	[2]									3,500	3,400	1,682	1,925	4,726	4,258	1,049	1,005	998	956
Total separate account assets	7,965		7,757												1,913	2,170	5,003	4,582	1,049	1,005
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance					1,011		943		1,005		750
Policyholder gains (losses)					22	[3]	9	[3]	29	[4]	27	[4]
Purchases, issuances, settlements:
Purchases					57		16		88		200
Sales					0		0		0		0
Settlements					(39)		(18)		(69)		(29)
Total purchases, sales, settlements					18		(2)		19		171
Transfers into/(out of) Level 3:
Transfers into Level 3					0		2		0		5
Transfers out of Level 3					(2)		0		(4)		(1)
Total transfers into/(out of) Level 3					(2)		2		(4)		4
Ending Balance					1,049		952		1,049		952
Policyholder Gains Losses Attributable To Instruments Still Held					$ 22		$ 9		$ 29		$ 22

[1] As of June 30, 2013, non-guaranteed separate accounts included $3.5 billion in assets supporting the Company's pension plans, including $998 million classified in Level 3.

[2] As of December 31, 2012, non-guaranteed separate accounts include $3.4 billion in assets supporting the Company's pension plans, including $956 million classified in Level 3.

[3] Included in this amount are gains of $22 million attributable to instruments still held at June 30, 2013 and gains of $9 million attributable to instruments still held at June 30, 2012.

[4] Included in this amount are gains of $29 million attributable to instruments still held at June 30, 2013 and gains of $22 million attributable to instruments still held at June 30, 2012