Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance	[1]	$ 49,343	$ 47,770		$ 47,585
Other comprehensive income (loss), net of tax		1,971	1,524		(583)
Total Equity, Ending Balance		54,041	49,343	[1]	47,770	[1]	$ 47,585	[1]
Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance	[1]	48,672	47,832		47,569
Total Equity, Ending Balance	[1]		48,672		47,832		47,569
Continuing Operations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), net of tax		1,856	1,520		(540)
Discontinued Operations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), net of tax		115	4		(43)
Debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance		1,067	(80)		277
Cumulative effect of adopting ASU 2018-02							59
Other comprehensive income (loss), net of tax		1,395	1,147		(416)
Total Equity, Ending Balance		2,462	1,067		(80)		277
Debt securities | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance					336
Total Equity, Ending Balance							336
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance		276	47		151
Cumulative effect of adopting ASU 2018-02							33
Other comprehensive income (loss), net of tax		383	229		(137)
Total Equity, Ending Balance		659	276		47		151
Cash flow hedge derivatives | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance					184
Total Equity, Ending Balance							184
Pension and other postretirement benefit plan adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance		(408)	(530)		(446)
Cumulative effect of adopting ASU 2018-02							(96)
Other comprehensive income (loss), net of tax		63	122		12
Total Equity, Ending Balance		(345)	(408)		(530)		(446)
Pension and other postretirement benefit plan adjustments | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance					(542)
Total Equity, Ending Balance							(542)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance		(21)	(43)		(68)
Cumulative effect of adopting ASU 2018-02							24
Other comprehensive income (loss), net of tax		15	22		1
Total Equity, Ending Balance		(6)	(21)		(43)		(68)
Other | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance					(44)
Total Equity, Ending Balance							(44)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance	[1]	799	(725)		(148)
Cumulative effect of adopting ASU 2018-02							6
Other comprehensive income (loss), net of tax		1,971	1,524		(583)
Total Equity, Ending Balance		2,770	799	[1]	(725)	[1]	(148)	[1]
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance	[1]	799	(725)		(142)
Total Equity, Ending Balance	[1]		799		(725)		(142)
Accumulated Other Comprehensive Income (Loss) | Continuing Operations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance		914	(606)		(86)
Cumulative effect of adopting ASU 2018-02							20
Other comprehensive income (loss), net of tax		1,856	1,520		(540)
Total Equity, Ending Balance		2,770	914		(606)		(86)
Accumulated Other Comprehensive Income (Loss) | Continuing Operations | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance					(66)
Total Equity, Ending Balance							(66)
Accumulated Other Comprehensive Income (Loss) | Discontinued Operations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance		(115)	(119)		(62)
Cumulative effect of adopting ASU 2018-02							(14)
Other comprehensive income (loss), net of tax		115	4		(43)
Total Equity, Ending Balance			$ (115)		(119)		(62)
Accumulated Other Comprehensive Income (Loss) | Discontinued Operations | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity, Beginning Balance					$ (76)
Total Equity, Ending Balance							$ (76)

[1] The par value of our preferred stock outstanding was less than $0.5 million at each date and, therefore, is excluded from this presentation.