Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013 item	Dec. 31, 2012 item
Available For Sale Securities In Unrealized Loss Position With Loss Severity Greater Than 20 Percent [Line Items]
Fair Value	$ 83,567	$ 82,901
Gross Unrealized Losses	329	320
Number of Securities	663	626
Fair Value Decline, Greater Than 20% [Member]
Available For Sale Securities In Unrealized Loss Position With Loss Severity Greater Than 20 Percent [Line Items]
Fair Value	403	444
Gross Unrealized Losses	165	198
Gross Unrealized OTTI	109	129
Number of Securities	134	148	[1]
Fair Value Decline, Greater Than 20% [Member] | Less Than Six Months [Member]
Available For Sale Securities In Unrealized Loss Position With Loss Severity Greater Than 20 Percent [Line Items]
Fair Value	46	34
Gross Unrealized Losses	22	9
Gross Unrealized OTTI	3	1
Number of Securities	16	14	[1]
Fair Value Decline, Greater Than 20% [Member] | Nine months or greater, but less than twelve months
Available For Sale Securities In Unrealized Loss Position With Loss Severity Greater Than 20 Percent [Line Items]
Fair Value		15
Gross Unrealized Losses		10
Number of Securities		3	[1]
Fair Value Decline, Greater Than 20% [Member] | Twelve Months Or Greater [Member]
Available For Sale Securities In Unrealized Loss Position With Loss Severity Greater Than 20 Percent [Line Items]
Fair Value	357	395
Gross Unrealized Losses	143	179
Gross Unrealized OTTI	$ 106	$ 128
Number of Securities	118	131	[1]

[1] We may reflect a security in more than one aging category based on various purchase dates.