Contingencies and Commitments (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Environmental Contingencies
Liability recorded for projected environmental remediation costs	$ 14,000,000
Guarantees Letters Of Credit [Abstract]
The range of expiration dates of guarantees made by the Parent Company	less than one year to more than 21 years
Obligations made by the Parent Company associated with non-recourse debt	24,000,000
Contingent Contractual Obligations [Line Items]
Amount	834,000,000
Number of Agreements	38
Commitments to invest in subsidiaries, excluding letters of credit	2,000,000
Litigation Contingencies
Aggregate reserves for claims deemed both probable and reasonably estimable	345,000,000	321,000,000
Loss Contingency Range Of Possible Loss Minimum	944,000,000
Loss Contingency Range Of Possible Loss Maximum	1,600,000,000
Guarantees
Contingent Contractual Obligations [Line Items]
Amount	577,000,000
Number of Agreements	20
Maximum Exposure Range for Each Agreement	<$1 - $231
Letters of credit under secured credit facility
Contingent Contractual Obligations [Line Items]
Amount	3,000,000
Number of Agreements	5
Maximum Exposure Range for Each Agreement	<$1 - $2
Letters of credit under secured credit facility | Minimum
Contingent Contractual Obligations [Line Items]
Letter of credit fees paid	0.25%
Letters of credit under secured credit facility | Maximum
Contingent Contractual Obligations [Line Items]
Letter of credit fees paid	3.25%
Cash Collateralized Letters Of Credit [Member]
Contingent Contractual Obligations [Line Items]
Amount	$ 254,000,000
Number of Agreements	13
Maximum Exposure Range for Each Agreement	<$1 - $169