Income Taxes - Continuing Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income taxes related to adjustments included in common shareholder’s equity:
Provision (benefit) for income taxes related to continuing operations	$ (114)	$ (129)	$ (200)	$ (28)	$ 42	$ 87	$ 112	$ (17)	$ (471)	$ 224	$ 325
Unrealized gains (losses) on securities available-for-sale, not other-than-temporarily impaired, net									0	0	(62)
Unrealized gains (losses) on other-than-temporarily impaired debt securities available-for-sale									0	0	(1)
Unrealized gains on cash flow hedging instruments									21	24	143
Changes in funded status of postretirement benefit plans									25	(2)	8
Foreign currency translation adjustments									0	0	(10)
Total income taxes									(425)	246	403
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current provision (benefit)									56	108	(917)
Deferred income tax provision (benefit)									(527)	116	1,242
Total income tax expense (benefit)	$ (114)	$ (129)	$ (200)	$ (28)	$ 42	$ 87	$ 112	$ (17)	(471)	224	325
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred income tax provision excluding the effects of other components									28	473	1,443
Increase in Federal operating loss carryforwards									(479)	(366)	(141)
Decrease in State valuation allowances									(171)	(53)	(51)
Decrease in State operating loss carryforwards and other temporary differences									95	42	11
(Increase) decrease in foreign and general business tax credits									0	20	(20)
Deferred income tax provision (benefit)									$ (527)	$ 116	$ 1,242