Derivatives and Hedging Activities (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash Flow Hedges
Derivatives designated as cash flow hedges	$ 0
Deferred loss on derivative instruments expected to be reclassified from accumulated other comprehensive income to earnings during the next 12 months	6
Rollforward of unrealized derivative losses included in accumulated other comprehensive income related to cash flow hedges
Net unrealized derivative losses at the beginning of the period	(21)	(26)
Reclassification of realized losses	2	2
Income tax benefit	(1)	(1)
Net unrealized derivative losses at the end of the period	(20)	(25)
Longest period of time over which the entity hedges exposure to the variability in future cash flows	6 years
2013
Summary of option premiums payable and receivable
Premiums Payable	287
Premiums Receivable	47
2014
Summary of option premiums payable and receivable
Premiums Payable	344
Premiums Receivable	54
2015
Summary of option premiums payable and receivable
Premiums Payable	317
Premiums Receivable	53
2016
Summary of option premiums payable and receivable
Premiums Payable	287
Premiums Receivable	46
2017
Summary of option premiums payable and receivable
Premiums Payable	237
Premiums Receivable	40
2018-2027
Summary of option premiums payable and receivable
Premiums Payable	780
Premiums Receivable	$ 104