Fair Value Measurements - Separate Account Assets (Details) (USD $) In Millions, unless otherwise specified					3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2013 Separate Accounts [Member]		Mar. 31, 2012 Separate Accounts [Member]		Mar. 31, 2013 Pension Benefits [Member]	Dec. 31, 2012 Pension Benefits [Member]	Mar. 31, 2013 Fair Value Inputs Level 1 [Member]	Dec. 31, 2012 Fair Value Inputs Level 1 [Member]	Mar. 31, 2013 Fair Value Inputs Level 2 [Member]	Dec. 31, 2012 Fair Value Inputs Level 2 [Member]	Mar. 31, 2013 Fair Value Inputs Level 3 [Member]	Dec. 31, 2012 Fair Value Inputs Level 3 [Member]	Mar. 31, 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	$ 557		$ 569								$ 247	$ 245	$ 310	$ 324	$ 0	$ 0
Non-guaranteed separate accounts	7,393	[1]	7,188	[2]					3,500	3,400	1,880	1,925	4,502	4,258	1,011	1,005	960	956
Total separate account assets	7,950		7,757								2,127	2,170	4,812	4,582	1,011	1,005
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at January 1,					1,005		750
Policyholder gains (losses)					7	[3]	18	[3]
Purchases, issuances, settlements:
Purchases					31		184
Sales					0		0
Settlements					(30)		(11)
Total purchases, sales, settlements					1		173
Transfers into/(out of) Level 3:
Transfers into Level 3					0		3
Transfers out of Level 3					(2)		(1)
Total transfers into/(out of) Level 3					(2)		2
Balance at March 31,					1,011		943
Policyholder Gains Losses Attributable To Instruments Still Held					$ 7		$ 12

[1] As of March 31, 2013, non-guaranteed separate accounts included $3.5 billion in assets supporting the Company's pension plans, including $960 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 $7 million attributable to instruments still held at March 31, 2013 and gains of $12 million attributable to instruments still held at March 31, 2012.