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Other Comprehensive Income, Cumulative OCI Balances (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Cumulative OCI balances [Abstract]
Balance, beginning of period	$ 197,066	$ 208,079
Balance, beginning of period adjusted balance				$ 197,055	$ 208,055
Other comprehensive income (loss), net of tax	2,173	(2,659)
Less: Other comprehensive income (loss) from noncontrolling interests	0	0
Balance, end of period	198,733	205,910
Accounting Standards Update 2017-08 [Member]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Transition Adjustment			$ (111)
Cumulative other comprehensive income [Member]
Cumulative OCI balances [Abstract]
Balance, beginning of period	(6,336)	(2,144)
Balance, beginning of period adjusted balance				(5,855)	(2,262)
Net unrealized gains (losses) arising during the period	2,147	(2,780)
Amounts reclassified from accumulated other comprehensive income	26	121
Other comprehensive income (loss), net of tax	2,173	(2,659)
Balance, end of period	(3,682)	(4,921)
Cumulative other comprehensive income [Member] \| Accounting Standards Update 2017-08 [Member]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Transition Adjustment				481
Cumulative other comprehensive income [Member] \| Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Transition Adjustment					(118)
Debt securities, parent [Member]
Cumulative OCI balances [Abstract]
Balance, beginning of period	(3,122)	171
Balance, beginning of period adjusted balance				(2,641)	53
Net unrealized gains (losses) arising during the period	2,136	(2,595)
Amounts reclassified from accumulated other comprehensive income	(61)	51
Other comprehensive income (loss), net of tax	2,075	(2,544)
Balance, end of period	(566)	(2,491)
Debt securities, parent [Member] \| Accounting Standards Update 2017-08 [Member]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Transition Adjustment				481
Debt securities, parent [Member] \| Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Transition Adjustment					(118)
Derivative and hedging activities, parent [Member]
Cumulative OCI balances [Abstract]
Balance, beginning of period	(685)	(418)
Balance, beginning of period adjusted balance				(685)	(418)
Net unrealized gains (losses) arising during the period	(26)	(182)
Amounts reclassified from accumulated other comprehensive income	60	45
Other comprehensive income (loss), net of tax	34	(137)
Balance, end of period	(651)	(555)
Defined benefit plans adjustments, parent [Member]
Cumulative OCI balances [Abstract]
Balance, beginning of period	(2,296)	(1,808)
Balance, beginning of period adjusted balance				(2,296)	(1,808)
Net unrealized gains (losses) arising during the period	(3)	4
Amounts reclassified from accumulated other comprehensive income	27	25
Other comprehensive income (loss), net of tax	24	29
Balance, end of period	(2,272)	(1,779)
Foreign currency translation adjustments, parent [Member]
Cumulative OCI balances [Abstract]
Balance, beginning of period	(233)	(89)
Balance, beginning of period adjusted balance				(233)	(89)
Net unrealized gains (losses) arising during the period	40	(7)
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income (loss), net of tax	40	(7)
Balance, end of period	(193)	(96)
Noncontrolling Interest [Member]
Cumulative OCI balances [Abstract]
Balance, beginning of period	900	1,143
Balance, beginning of period adjusted balance				$ 900	$ 1,143
Less: Other comprehensive income (loss) from noncontrolling interests	0	0
Balance, end of period	901	958
AOCI Attributable to Noncontrolling Interest [Member]
Cumulative OCI balances [Abstract]
Less: Other comprehensive income (loss) from noncontrolling interests	0	0
Debt securities, noncontrolling interest [Member]
Cumulative OCI balances [Abstract]
Less: Other comprehensive income (loss) from noncontrolling interests	0	0
Derivative and hedging activities, noncontrolling interest [Member]
Cumulative OCI balances [Abstract]
Less: Other comprehensive income (loss) from noncontrolling interests	0	0
Defined benefit plans adjustments, noncontrolling interest [Member]
Cumulative OCI balances [Abstract]
Less: Other comprehensive income (loss) from noncontrolling interests	0	0
Foreign currency translation adjustments, noncontrolling interest [Member]
Cumulative OCI balances [Abstract]
Less: Other comprehensive income (loss) from noncontrolling interests	$ 0	$ 0